Kids Research Express

Chimpanzee

2011-02-19T18:01:00.000-08:00

Chimpanzee, an ape, genus Pan, of the equatorial forests of central and W Africa. The common chimpanzee, Pan troglodytes, lives N of the Congo River. Full-grown animals of this species are up to 5 ft (1.5 m) tall and weigh about 150 lb (68 kg); they have an arm spread of up to 9 ft (2.7 m) and are much stronger than humans. They are covered with long, black hair over most of the body and have naked faces ranging in color from nearly white to nearly black. The pygmy chimpanzee, P. paniscus, now usually called the bonobo, lives south of the Congo. It is a bit smaller and more slenderly built, with a black face.

Chimpanzees spend much time on the ground, where they walk on all fours, using the soles of the feet and the knuckles of the hands; they can also stand on two legs and sometimes walk this way for short distances. They climb trees in pursuit of food and for nesting and can swing by their hands from branch to branch. Their diet consists largely of fruit and other plant matter, but they also hunt and eat small animals, including monkeys. They use and even make primitive tools; for example, they collect termites using twigs and crack nuts using stones. Many primatologists now attribute culture to chimpanzees, noting learned variations in such skills and habits among different groups.

Chimpanzees move about the forest in bands of varying composition, usually numbering six to ten individuals. The males of a group engage in dominance contests involving much screaming and stamping. Family groups consist of mothers and offspring; females mate with many males during their fertile periods. A single infant is born every three to eight years; young chimpanzees ride about on their mothers' backs. Under ideal circumstances chimpanzees may live 50 years.

Although incapable of speech beyond their own simple vocalizations, captive chimpanzees have been taught to communicate in a language using visual rather than verbal symbols. Because of their close evolutionary relationship to humans they are often used for medical and behavioral experimentation, but the degree to which chimpanzees and humans are genetically close is a subject of dispute, with estimates of the amount of DNA the species share ranging from 94.6% to 99.4%. Chimpanzees, especially bonobos, are considered endangered species because of hunting and loss of habitat.

Chimpanzees are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Primates, family Pongidae.

Insect

2011-02-19T17:57:00.000-08:00

Insect, invertebrate animal of the class Insecta of the phylum Arthropoda. Like other arthropods, an insect has a hard outer covering, or exoskeleton, a segmented body, and jointed legs. Adult insects typically have wings and are the only flying invertebrates.

The body of the typical adult insect is divided into three distinct parts, the head, thorax, and abdomen. The head bears three pairs of mouthparts, one pair of compound eyes, three simple eyes (ocelli), and one pair of jointed sensory antennae. The thorax is divided into three segments, each with a pair of jointed legs, and bears two pairs of wings. The abdomen has posterior appendages associated with reproduction. The exoskeleton is composed of a horny substance called chitin.

Insects breathe through a complex network of air tubes (tracheae) that open to the outside through a series of small valved apertures (spiracles) along the sides of the body. In chewing insects the digestive system includes a muscular gizzard that is lacking in sucking insects. The simple circulatory system is composed of a tubular heart that pumps blood forward into the head, from which it diffuses through the tissues and back into the heart. The aquatic larvae of many insects breathe by means of external gills; some very primitive species breathe directly through the body wall.

Insect Species

There are about 900,000 known insect species, three times as many as all other animal species together, and thousands of new ones are described each year. They are commonly grouped in 27 to 32 orders, depending upon the classification used. The largest order is that of the beetles (Coleoptera). Next, in order of size, are the moths and butterflies (Lepidoptera); the wasps, ants, and bees (Hymenoptera); and the flies and mosquitoes (Diptera). Other major orders are the true bugs (Hemiptera); the cicadas, aphids, and scale insects (Homoptera); the grasshoppers and crickets (Orthoptera); the cockroaches (Blattodea); and the mantids (Mantodea).

Insects are found throughout the world except near the poles and pervade every habitat except the sea (although there is one marine species of water strider). Fossil records indicate that many species exist today in much the same form as they did 200 million years ago. Their enormous biological success is attributed to their small size, their high reproductive rate, and the remarkable adaptive abilities of the group as a whole, shown by the enormous variety in body structure and way of life. The mouthparts may be adapted to chewing, sucking, piercing, or lapping and the legs for walking, running, jumping, burrowing, or swimming. Insects may feed on plants or decaying matter or prey upon other small animals (especially other insects) or parasitize larger ones; they may be omnivorous or highly specialized in their diets. They display a remarkable variety of adaptive shapes and colors that may serve either as camouflage or as warning (see mimicry). Some have stinging spines or hairs and blistering or noxious secretions, used for defense.

Reproduction

A few species, notably the fireflies, produce light, used as a signal in courtship, by a chemical reaction. The sexes are separate in insects, and reproduction is usually sexual, although in many insect groups eggs sometimes develop without fertilization by sperm (see parthenogenesis). In some insects, such as bees, unfertilized eggs become males and fertilized eggs females. In others, such as aphids, all-female generations are produced by parthenogenesis. Eggs are usually laid in a sheltered place; in a few insects they are retained and hatched internally. After hatching, the insect must molt periodically as it grows, since the rigid exoskeleton does not allow much expansion. A new, soft exoskeleton forms beneath the old one, and after each molt the insect undergoes a rapid expansion before its new covering hardens. The stages between molts are called instars; the final instar is the adult.

Trilobite

2011-02-19T17:17:00.000-08:00

Trilobite (trī`ləbīt'), subphylum of the phylum Arthropoda that includes a large group of extinct marine animals that were abundant in the Paleozoic era. They represent more than half of the known fossils from the Cambrian period. The trilobite body was generally oval and flat and was divided into three roughly equal sections: the head, thorax, and tail. The name trilobite refers to a pair of furrows along the length of the animal that divided the body into three longitudinal regions. The body was covered by a mineralized shell. Because the dorsal, or upper, shell was thicker than the under shell, it has been the part best preserved in fossil form. Trilobites were abundant inhabitants of the Cambrian and Ordovician geological periods. They declined thereafter, possibly because they became food for cephalopods and later for fish, and became extinct in the Permian period. Trilobites are most closely related to the chelicerates, which include the horseshoe crabs and spiders.

Mastodon

2011-02-19T17:14:00.000-08:00

Mastodon (măs`tədŏn'), name for a number of prehistoric mammals of the extinct genus Mammut, from which modern elephants are believed to have developed. The earliest known forms lived in the Oligocene epoch in Africa. These were long-jawed mastodons about 4 1-2 ft (137 cm) high, with four tusks and a greatly elongated face. Their descendants in the Miocene epoch were the size of large elephants, the latest forms having long, flexible trunks, like those of elephants, and only two tusks. During Miocene times they spread over Europe, Asia, and North America. The mastodons were forest dwellers; they obtained their food by browsing and their teeth were more numerous and of a simpler form than those of the elephant. They were apparently extinct in the Old World by the early Pleistocene epoch but survived in North America until late Pleistocene times. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Proboscidae, family Mammutidae.

Species

2011-02-19T17:10:00.000-08:00

Species, in biology, a category of classification, the original and still the basic unit in the demarcation of plant and animal types. The species marks the boundary between populations of organisms rather than between individuals. Because related species are not absolutely permanent (see evolution), a precise definition of the term is difficult. On the basis of genetics, scientists now include in a species all individuals that are potentially or actually capable of interbreeding and that share the same gene pool. The latter term refers to that collection of characteristics whose combination is unique in the species, although each individual of the group may not display every single one of the characteristics (see genetics). In the few cases where members of different species can interbreed, the offspring are usually sterile (e.g., the mule). Groups distinguished by lesser differences than those marking a species are called variously subspecies, varieties, races, or tribes.

See: Species and Speciation

Mammoth

2011-02-19T17:01:00.001-08:00

Mammoth, name for several large prehistoric elephants of the extinct genus Mammuthus, which ranged over Eurasia and North America in the Pleistocene epoch. The shoulder height of the Siberian, or woolly, mammoth, which roamed throughout the Northern Hemisphere, was about 9 ft (2.7 m), and that of the imperial mammoth of the North American Great Plains was up to 13 1-2 ft (4.1 m). Mammoths were covered by a long, shaggy, black outer coat and a dense, woolly undercoat. They had complex, many-ridged molar teeth; long, slender upward-curved tusks; and a long trunk. Ivory hunters have collected their tusks for centuries in Siberia, where some 50,000 have been discovered; it is from these and from the drawings left by the Cro-Magnon people in the caves of S France that the mammoth's appearance is known. Paleolithic (Old Stone Age) people hunted mammoths, as is evidenced by remains of the animals found together with tools, and may have contributed to their extinction. Mammoths are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Proboscidea, family Elephantidae.

Photos of Mammals

2010-10-09T19:47:00.000-07:00

Aardwolf
The aardwolf, a member of the hyena family, is found throughout southern and eastern Africa. Aardwolves travel at night hunting for food, which consists of carrion (dead and decaying animal flesh) and insects, usually termites. They have weak jaws and small teeth, leaving them without defenses against enemies such as dogs.

Abyssinian
Abyssinians are particularly affectionate and have fine, soft fur resembling that of a wild rabbit. The origin of the cat is unknown, although its appearance suggests a relationship to the cats of ancient Egypt. It is one of the oldest breeds of domesticated cat.

Afghan Hound
The Afghan hound, similar to the greyhound, originated in Afghanistan and was known in ancient Egypt. A capable hunting dog, the Afghan hound is a swift runner and a powerful jumper.

African Elephants
African elephants live in grassy regions south of the Sahara Desert. Bull (male) elephants stand about 3.4 m (11 ft) tall and weigh about 5.4 metric tons, while cow (female) elephants stand 2.8 m (9 ft) tall and weigh about 3.6 metric tons. They have no sweat glands, so they like to cool off by rolling in ponds and streams. The mud that dries on their skin protects it from the sun.

Agouti
A large rodent common to the forests of Central America and central-northern South America, the swift, ground-dwelling agouti feeds on leaves, roots, and fallen fruit. The agouti is hunted by farmers because it destroys crops in agricultural areas.

Akhal-Teké
A prized desert horse, the Akhal-Teké has been bred and raised for at least 3000 years, and may have been an ancestor of the Arabian. Remarkable endurance and resistance to heat give the powerful yet graceful Akhal-Teké an edge in competitive long-distance riding and show jumping.

Alaskan Malamute
This Alaskan Malamute has dense, layered fur as a shield from severe weather. The nomadic Mahlemuts, an Inuit people of northwestern Alaska, first bred the Alaskan Malamute as a sled dog to haul their belongings. Ranging from light gray to black in color, Alaskan Malamutes are also popular as pets and show dogs.

Alpine Ibex
Famous for its surefootedness in steep, rocky terrain, the Alpine ibex is one of four species of mountain goat in the genus Capra. The Alpine ibex was on the brink of extinction from overhunting and habitat destruction in the early 20th century, but is now protected and rebuilding herd populations in Italy’s Gran Paradiso National Park and other European wildlife preserves.

American Black Bear
The American black bear lives in forests throughout North America, from Alaska and Canada to mountains in northern Mexico. Unlike most other bear species, the American black bear has adapted to human encroachment on its habitat, and it is able to survive in populated suburban areas. Despite the bear’s common name, the color of the American black bear ranges from black to brown, cinnamon, beige, and even pure white.

Antarctic Fur Seal
The Antarctic fur seal is one of 14 species of eared seals. Fur seals are polygamous and assemble in huge breeding colonies beginning in October. Breeding females feed exclusively on small, shrimplike crustaceans called krill, whereas males feed on krill, penguins, and fish. Although most eared seal populations have been decimated by overhunting, the Antarctic fur seal has rebounded from near extinction in the late 1800s to a current population of between 700,000 and 1 million animals.

more pictures

Coral

2009-04-15T22:50:00.001-07:00

Coral, common name for members of a large class of marine invertebrates characterized by a protective calcium carbonate or horny skeleton. This protective skeleton is also called coral. Corals are divided into two subclasses, based on differences in their radial symmetry (symmetry around a central axis). One subclass consists of colonial, eight-tentacled animals, each with an internal skeleton. Among them are whip corals, gorgonians, and the red coral used in making jewelry. Members of the other subclass commonly have six tentacles, or multiples of six, but other patterns are also observed. They include the stony, or true, corals. Another class of the same phylum also contains forms known as coral that are not considered here.

STRUCTURE
True corals secrete calcium carbonate from the bottom half of the stalk of the individual animal, or polyp, forming skeletal cups to which the polyps are anchored and into which they withdraw for protection. In the flattened oral disc at the top of the stalk is an opening, edged with feathery tentacles and cilia, that is both mouth and anus. At night the tentacles extend from the cup, seize animal plankton that wash against them, and carry the food to the mouth. Stinging cells, or nematocysts, on the tentacles can also paralyze prey.

COLONIES
Some scleractinians exist as solitary polyps, but the majority are colonial. Colonial polyps average from 1 to 3 mm (0.04 to 0.12 in) in diameter. They are connected laterally by tubes that are an extension of the polyps' gastrovascular cavities, and the colony grows by asexual budding from the base or the oral disc of the polyps. Living polyps build on the deposits of their predecessors; the wide range of branched or massive forms that result depends on the species involved.

Colonial corals can grow in deep water, but reef-building corals are found only in warm, shallow seas. They live no deeper than light can penetrate because the symbiotic algae called zooxanthellae that live in their tissues require light for photosynthesis, and the corals cannot exist without the algae. Carbon is passed by the algae to the coral, increasing its energy, and the food caught by the coral may supply nitrogen and phosphorus for both organisms. The dependence of the corals on the algae probably varies according to species and locality. Scleractinian corals are the main contributors to a reef, but other organisms also add to it, such as hydrozoan corals, calcareous algae, mollusks, and sponges. See Coral Reef.

Scientific classification: Corals belong to the class Anthozoa in the phylum Cnidaria. Corals with eight tentacles make up the subclass Ostocorallia or Alcyonaria. Corals that commonly have six tentacles or multiples of six belong to the subclass Zoantharia (or Hexacorallia). Stony, or true, corals belong to the order Scleractinia (or Madreporaria).

Silkworm

2008-10-18T22:08:00.000-07:00

Silkworm, common name for the silk-producing larvae of any of several species of moths. Silkworms possess a pair of specially modified salivary glands called silk glands, or sericteries, which are used in the production of cocoons. The silk glands secrete a clear, viscous fluid that is forced through openings, called spinnerets, on the mouthparts of the larva; the fluid hardens as it comes into contact with air. The diameter of the spinneret determines the thickness of the silk thread produced.

The best-known silkworm is the larvae of the common, domesticated silkworm moth. This moth, native to China, was introduced into Europe and western Asia in the 6th century ad and into North America in the 18th century. The moth has been cultivated for many centuries and is no longer known in the wild state. Breeders have produced many varieties of the moth, the most important of which produce three broods of young annually.

A typical adult silkworm moth is yellow or yellowish-white, with a thick, hairy body, and has a wingspread of about 3.8 cm (about 1.5 in). The adult has rudimentary mouthparts and does not eat during the short period of its mature existence; the female dies almost immediately after depositing the eggs, and the male lives only a short time thereafter. The female deposits 300 to 400 bluish eggs at a time; the eggs are fastened to a flat surface by a gummy substance secreted by the female. The larvae, which hatch in about ten days, are about 0.6 cm (about 0.25 in) long. The larvae feed on leaves of white mulberry, Osage orange, or lettuce. Silkworm caterpillars (see Caterpillar) that are fed mulberry leaves produce the finest quality silk. Mature larvae are about 7.5 cm (about 3 in) long and yellowish-gray or dark gray in color.

About six weeks after hatching, the common silkworm stops eating and spins its cocoon. The length of the individual fiber composing the cocoon varies from 300 to 900 m (1000 to 3000 ft). The silkworm pupates for about two weeks; if allowed to complete its pupation period, it emerges as an adult moth. Tearing during emergence damages the silken cocoon beyond commercial use. Therefore, in the commercial production of silk, only enough adult moths are allowed to emerge to ensure continuation of the species. Most of the silkworms are killed by heat, either by immersion in boiling water or by drying in ovens.

Other moths known as silkworm moths include the giant silkworm moths. The larvae of these large moths also spin silken cocoons, but they are less widely used for commercial silk production.

Scientific classification: Silkworms belong to the order Lepidoptera. The domesticated silkworm moth makes up the family Bombycidae and is classified as Bombyx mori. The giant silkworm moths make up the family Saturniidae.

Urinary System of the Animals

2008-09-21T05:17:00.000-07:00

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All vertebrates dispose of excess water and other wastes by means of kidneys. The kidneys of fish and amphibians are comparatively simple, while those of mammals are the most complex. Fish and amphibians absorb a great deal of water and, as a result, must excrete large quantities of urine. In contrast, the urinary systems of birds and reptiles are designed to conserve water; these animals produce urine that is solid or semisolid.

Reproductive System of Animals

2008-09-21T05:12:00.000-07:00

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In many invertebrate species individual animals bear both testes and ovaries (see Hermaphroditism). In some invertebrates, and in most vertebrates, individuals bear either testes or ovaries, but not both sets of organs. In invertebrates, a single animal may have as many as 26 pairs of gonads; in vertebrates, the usual number is 2. Cyclostomes and most birds are unusual among vertebrates in possessing only a single gonad; owls, pigeons, hawks, and parrots are unusual among birds in having two gonads. The size of gonads increases at sexual maturity because of the great number of germ cells produced at that time; many germ cells are also produced during breeding seasons so that many animals have a seasonal increase in size of the gonads. During the breeding season of fish, the ovaries increase in size until they constitute about one-quarter to one-third of the total body weight.

The testes and ovaries of mature animals differ greatly in structure. The testes are composed of delicate convoluted tubules, known as seminiferous tubules, in which the primitive germ cells mature into spermatozoa. The testes of mammals are generally oval bodies, enclosed by a capsule of tough connective tissue. Projections from this tough capsule into the testis divide the testis into several compartments, each of which is filled with hundreds of seminiferous tubules. The mature spermatozoa are discharged through a number of ducts, called the efferent ducts, which communicate with the epididymis, a thick-walled, coiled duct in which the sperm are stored.

In all vertebrates below marsupials on the zoological scale, and in elephants, sea cows, and whales, the testis remains within the body cavity during the lifetime of the animals. In many mammals, such as rodents, bats, and members of the camel family, the testis remains within the body cavity during periods of quiescence, but moves into an external pocket of skin and muscle, known as the scrotum, during the breeding season. In marsupials, and in most higher mammals, including the human male, the testes are always enclosed in an external scrotum. During fetal life, the testes move through the muscles composing the posterior, ventral portion of the trunk and carry with them the portion of the peritoneum and skin surrounding these muscles. The channel in the muscles through which the testis moves is known as the inguinal canal; it usually closes after birth, but sometimes remains open and is then often the site of herniation (see Hernia). The portion of the peritoneum that the testis carries with it forms a double wall of membrane between the scrotum and testis and is known as the tunica vaginalis. Occasionally, the testes in the human male do not descend into the scrotal sac; this condition of nondescent, which is known as cryptorchidism, may result in sterility if not corrected by surgery or the administration of hormones. Retention of the testes within the body cavity subjects the germ cells to temperatures that are too high for their normal development; the descent of the testes into the scrotum in higher animals keeps the testes at optimum temperatures.

Respiratory Systems in Other Animals

2008-09-21T05:06:00.000-07:00

The need to take in oxygen and expel carbon dioxide is almost universal among organisms. The movement of these gases between an organism and its environment, called gas exchange, is accomplished in a variety of ways by different organisms. In one-celled aquatic organisms, such as protozoans, and in seaweeds, sponges, jellyfish, and other aquatic organisms that are only a few cell layers thick, oxygen and carbon dioxide diffuse directly between the water and cells. Diffusion works for these simple organisms because all cells of the organism are within a few millimeters of an oxygen source.

Animals with many cell layers cannot rely on diffusion because cells several layers deep in the body would die before oxygen reached them. As a result, for gas exchange, more-complex animals require special respiratory organs, such as gills or lungs, in combination with circulatory structures, such as blood, blood vessels, and a heart. The earliest development of these gas exchange structures is seen in roundworms, microscopic invertebrates abundant in water and moist soil. In roundworms, oxygen diffuses through the skin into a fluid that fills an internal cavity. As the worm moves, the fluid sloshes around in the cavity, bringing oxygen into contact with the digestive system, reproductive organs, and other structures in the cavity. This primitive circulatory system is called an open circulatory system because the fluid is not contained within vessels. In clams an open circulatory system is combined with a heart that pumps fluid around the internal cavity. Clams also use gills, thin-walled filaments that are extensions of the body surface. Gills provide a more extensive surface area for gas exchange than the body surface alone, enabling clams and larger organisms to obtain the amount of oxygen they need. Fish have gills, a heart, and a closed circulatory system, one in which blood is transported in vessels by the pumping action of the heart.

Relatively simple land-dwelling organisms, including some plants, fungi, and animals such as flatworms, accomplish gas exchange by diffusion. More-complex organisms, however, rely on specialized respiratory structures. Instead of gills, whose delicate filaments collapse unless supported by water, land animals use lungs. Located inside the body, lungs are formed by the infolding of membranes. The folds form a single balloon-like sac, as in amphibians; they may be arranged in stacks, as in the book lungs of spiders; or they are composed of millions of tiny air sacs, such as the lungs of most mammals. In virtually all vertebrates, a heart and a closed circulatory system work with the lungs to deliver oxygen and to remove carbon dioxide from cells.

Insects have a unique respiratory system made up of small tubes called tracheae. The tracheae connect all parts of the body to small openings on the surface of the insect. Oxygen and carbon dioxide are transported through the tracheae, and from the tracheae to the blood of the insect by diffusion. The blood of most insects is contained in an open circulatory system and is moved around the internal organs by a heart.

The respiratory system of birds, adapted for flight, is very different from that of land-bound animals. The lungs have two openings, one for taking in oxygen-filled air; the other for expelling carbon dioxide-laden air. Rather than ending up in alveoli, the air loops through the lungs so that the oxygen flow through the lungs is continuous. This design enables birds to obtain the amount of oxygen they need to power the extremely high energy demands of flight.

The Vertebrate Nervous System

2008-09-21T04:55:00.000-07:00

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Vertebrate Brains
Although all vertebrate brains share the same basic three-part structure, the development of their constituent parts varies across the evolutionary scale. In fish, the cerebrum is dwarfed by the rest of the brain and serves mostly to process input from the senses. In reptiles and amphibians, the cerebrum is proportionally larger and begins to connect and form conclusions about this input. Birds have well-developed optic lobes, making the cerebrum even larger. Among mammals, the cerebrum dominates the brain. It is most developed among primates, in whom cognitive ability is the highest.

Vertebrate animals have a bony spine and skull in which the central part of the nervous system is housed; the peripheral part extends throughout the remainder of the body. That part of the nervous system located in the skull is referred to as the brain; that found in the spine is called the spinal cord. The brain and the spinal cord are continuous through an opening in the base of the skull; both are also in contact with other parts of the body through the nerves. The distinction made between the central nervous system and the peripheral nervous system is based on the different locations of the two intimately related parts of a single system. Some of the processes of the cell bodies conduct sense impressions and others conduct muscle responses, called reflexes, such as those caused by pain (see Reflex).

In the skin are cells of several types called receptors; each is especially sensitive to particular stimuli. Free nerve endings are sensitive to pain and are directly activated. The neurons so activated send impulses into the central nervous system and have junctions with other cells that have axons extending back into the periphery. Impulses are carried from processes of these cells to motor endings within the muscles. These neuromuscular endings excite the muscles, resulting in muscular contraction and appropriate movement. The pathway taken by the nerve impulse in mediating this simple response is in the form of a two-neuron arc that begins and ends in the periphery. Many of the actions of the nervous system can be explained on the basis of such reflex arcs, which are chains of interconnected nerve cells, stimulated at one end and capable of bringing about movement or glandular secretion at the other.

Digestive Systems of Animals

2008-09-21T04:49:00.000-07:00

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The simplest invertebrates (animals without backbones) do not have specialized digestive organs. Single-celled organisms, such as amoebas, rely on intracellular digestion (digestion within the cell). Some many-celled organisms, such as the sponge, also use intracellular digestion. The sponge obtains the tiny organic particles that make up its diet from water passing through its body. Water enters through the sponge’s pores and leaves through an opening called the osculum. As water flows through the interior canals of the sponge, specialized cells that line these canals, called collar cells, catch and engulf organic matter. Inside the collar cells, sacs called vacuoles form around the food and enzymes digest it. The digested food then passes to other cells in the sponge’s body.

Intracellular digestion meets the needs of simple animals, but more complex organisms require systems that are more specialized. Animals such as jellyfish and nonparasitic flatworms combine the intracellular process with some specialized digestive organs. These animals have a definite mouth and a saclike cavity, which is lined with digestive cells that secrete enzymes. Digestion begins when the enzymes break down food inside the cavity in an extracellular (outside the cell) process. Cells then engulf the partly digested food, and an intracellular process similar to that of sponges completes digestion. Wastes are excreted through the mouth.

Most of the more complex invertebrates and all vertebrates (animals with a backbone) digest food entirely through extracellular processes. Food moves in one direction, from mouth to anus, through the series of organs that make up the alimentary canal. Specialization of various parts of the alimentary canal improves the body’s ability to break down food and absorb various kinds of nutrients. The mouth of many animals contains teeth or other structures to break up large lumps of food. Behind the mouth, the pharynx and esophagus swallow the food and move it to the stomach. The stomach temporarily stores the food, mixes it with digestive juices, and carries out some digestion.

Digestion is completed in the intestine. The liver and pancreas pour their digestive juices into the anterior (front) end of this organ. After the anterior intestine absorbs the usable products of digestion, the walls of the posterior (rear) intestine absorb leftover water. In vertebrates the anterior intestine is called the small intestine; the posterior intestine is the large intestine. Feces, composed of unabsorbed and indigestible food residues, form in the posterior intestine, where they are stored until they are excreted through the anus.

Within this basic plan, the specific components of the digestive system vary enormously from one animal to another. For example, a fish’s pharynx contains gill slits for breathing but has no digestive function. An earthworm’s stomach consists of two organs: a crop, in which food is stored, and a muscular gizzard, which carries out mechanical digestion by grinding food against particles of sand. The stomachs of ruminant mammals, such as cattle and deer, consist of three or four compartments, each performing a specific function. Amphibians, reptiles, and birds have an organ called a cloaca, which serves as an exit for both digestive wastes and sex cells.

Circulatory Systems in Non-Humans

2008-09-21T04:45:00.000-07:00

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One-celled organisms and many simple multicelled animals, such as sponges, jellyfishes, sea anemones, flatworms, and roundworms, do not have a circulatory system. All of their cells are able to absorb nutrients, exchange gases, and expel wastes through direct contact with either the outside or with a central cavity that serves as a digestive tract.

More complex invertebrates have a wide range of circulatory system designs. These invertebrate circulatory systems are classified as either open or closed. Open systems—found in starfishes, clams, oysters, snails, crabs, insects, spiders, and centipedes—lack capillaries, and the blood bathes the tissues directly. In closed systems, the blood is confined to a system of blood vessels. Invertebrates with closed systems include segmented worms, squids, and octopuses.

All vertebrate animals have closed circulatory systems. These systems are classified by the number of chambers in the heart, which determines the basic configuration of blood flow. Fish have two-chambered hearts with one atrium and one ventricle. Blood pumped from the ventricle travels through arteries to the gills, where it diverges into capillaries and exchanges gases. Leaving the gills, the capillaries reconvene into blood vessels that carry the oxygenated blood to the rest of the body, where the vessels again diverge into capillaries before reconvening into veins that return to the heart. In this way, the blood passes through first the respiratory organs (the gills) and then the systemic circulation between each pass through the heart.

Frogs and amphibians have three-chambered hearts, with two atriums and one ventricle. Blood pumped from the ventricle enters a forked artery. One fork, the pulmonary circulation, leads to the lung. The other fork, the systemic circulation, leads to the rest of the body. Blood returning from the pulmonary circulation enters the left atrium, while blood from the systemic circulation enters the right atrium. Although there is some mixing of oxygenated and deoxygenated blood in the ventricle, a ridge within the ventricle assures that most of the oxygenated blood is diverted to the systemic circulation and most of the deoxygenated blood goes to the pulmonary circulation. In reptiles, this ridge is more developed, forming a partial wall. In crocodiles, the wall is complete, forming a four-chambered heart like that found in mammals and birds.

Aquaculture

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Aquaculture, farming of aquatic organisms in fresh, brackish or salt water. A wide variety of aquatic organisms are produced through aquaculture, including fishes, crustaceans, mollusks, algae, and aquatic plants. Unlike capture fisheries, aquaculture requires deliberate human intervention in the organisms' productivity and results in yields that exceed those from the natural environment alone. Stocking water with seed (juvenile organisms), fertilizing the water, feeding the organisms, and maintaining water quality are common examples of such intervention.

Most aquacultural crops are destined for human consumption. However, aquaculture also produces bait fishes, ornamental or aquarium fishes, aquatic animals used to augment natural populations for capture and sport fisheries (see Fishing), algae used for chemical extraction, and pearl oysters and mussels, among others.

Aquaculture is considered an agricultural activity, despite the many differences between aquaculture and terrestrial agriculture. Aquaculture mainly produces protein crops, while starchy staple crops are the primary products of terrestrial agriculture. In addition, terrestrial animal waste can be disposed of off-site, whereas in aquaculture such waste accumulates in the culture environment. Consequently, aquaculturists must carefully manage their production units to ensure that water quality does not deteriorate and become stressful to the culture organisms.

Ruminant

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Ruminant, even-toed animal that regurgitates and masticates its food after swallowing. The majority of ruminants have four nipples; they usually have sweat glands only on the muzzle and between the toes. Most species bear horns that may be permanent or may be shed periodically. The division includes three subdivisions: Tragulina, containing the chevrotains and characterized by a stomach with three chambers; Tylopoda, consisting of the camel, dromedary, llama, alpaca, guanaco, and vicuña, and characterized by a stomach with three distinct chambers; and Pecora, containing all sheep, goats, antelope, deer, gazelles, giraffes, and domestic cattle, and characterized by the presence of a distinct four-chambered stomach. Pecoran animals are known as true ruminants. Between the esophagus and the intestine, the stomach chambers of a true ruminant are the rumen, the reticulum, the omasum, and the abomasum, or rennet bag.

Scientific classification: Ruminants make up the suborder Ruminantia of the order Artiodactyla.

Amoeba

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Amoeba, any of a group of unicellular organisms characterized by their locomotive method of extending cytoplasm outward to form pseudopodia (false feet). The amoeboid group includes hundreds of different organisms, ranging in size from about .25 to 2.5 mm (about 0.0098 to 0.098 in). Amoebas are considered the most primitive animals and are classified in the kingdom Protista. All amoeboid organisms have thin cell membranes, a semirigid layer of ectoplasm, a granular, jellylike endoplasm, and an oval nucleus. Some species live on aquatic plants and some in moist ground; others are parasitic in animals.

Amoebas also use pseudopodia for feeding. Chemical stimuli from smaller organisms, the amoeba's food, induce the formation of pseudopodia, pairs of which envelop the organism, at the same time forming a cavity, or vacuole. A digestive enzyme secreted into the cavity breaks down this food into soluble chemical substances that then diffuse from the cavity into the cytoplasm. Undigested food and wastes are excreted through the ectoplasm, which also absorbs oxygen from the surrounding water and eliminates carbon dioxide, a by-product of metabolism, in a form of respiration. After a period of growth, the amoeba reproduces by splitting into two equal parts.

At least six forms of amoeba are parasitic in humans. Most important of these is Entamoeba histolytica, which causes amebiasis and dysentery. The diseases often occur in epidemics when raw sewage contaminates water supplies or when soil is fertilized with untreated human wastes.

Sipuncula

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Peanut Worm, common name for small, unsegmented marine worms having bulb-shaped bodies and bearing crowns of tentacles on long, slender, processes, called introverts, that can turn inside out. Peanut worms are common but inconspicuous, frequently nestling among shells; they can burrow, but they move slowly. The main part of the body contains a single cavity (the coelom) filled with fluid under pressure from the body musculature. When the introvert turns inside out, the tentacles at its tip are used for feeding on small particles of organic matter. The placement of peanut worms in the animal kingdom is uncertain, but they are probably close to the annelid worms. Little structural diversity exists within the group; about 250 species have been described.

Scientific classification: Peanut worms make up the phylum Sipuncula.

Rotifera

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Rotifer, any of a phylum of multicellular, generally microscopic, aquatic animals that are abundant worldwide, and are most frequently found in freshwater bogs, ponds, and puddles. Rotifers vary in shape but always have retractable, hairlike crowns of cilia that, in motion, resemble turning wheels. (Among the first microscopic life forms to be studied, they were commonly known as wheel animalcules.) The animals can attach themselves temporarily to surfaces by means of a cementing secretion from the “foot” of the body. They reproduce sexually, but males are rare; except under severe conditions, the eggs develop parthenogenetically. Rotifers feed on other microorganisms; a few species are parasitic.

Scientific classification: Rotifers make up the phylum Rotifera.

Porifera

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Sponge, any of several thousand species constituting a phylum of simple invertebrate animals. Sponges are mainly marine, with a few freshwater species. They are abundant throughout the world and especially in tropical waters, where they and other invertebrates such as corals are important in the formation of calcareous deposits.

The structural components of a sponge include the outer, protective layer of cells and the spiny spicules, which form the skeleton. Sponges feed off microorganisms in the water that flow in through small openings known as ostia. The flagella on the inner layer of cells move the water through the sponge, absorbing food particles as the water flows past. Eventually the water exits through the osculum, the cavity at the top of the sponge.

Scientific classification: Sponges make up the phylum Porifera. Four major groups exist. All the Calcarea are marine, with skeletal spicules composed of calcium carbonate. The Hexactinellida are found in the deep sea; because their skeleton is made of silica in beautiful six-pointed arrangements, they are called glass sponges. The Demospongiae (95 percent of all living species) include the few freshwater forms. Their skeletal network is made of spongin, a rather flexible protein material (that of a bath sponge made from a real sponge), and in some species silica spicules are also present. The Demospongiae include the carnivorous Mediterranean sponge, which is classified as Asbestopluma hypogea. The Sclerospongiae have a combination of a thin silica and spongin skeleton that surrounds a larger, central calcareous skeleton.

Pogonophora

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Pogonophore, also beardworm, any member of a phylum of deep-ocean animals resembling worms that feed by means of long, hollow tentacles, each with a double row of hair-like cilia. Pogonophores live in tubes they secrete in ocean-bottom oozes, sometimes near hydrothermal vents. The animals may be more than 30 cm (more than 1 ft) long but are never more than about 2 mm (about 0.08 in) in diameter. The body has no digestive tract, and food is absorbed directly through a front region bearing up to 250 tentacles. The sexes are separate. Pogonophores were first discovered in Indonesia in 1900. Their relationship to other phyla is not yet certain, although they are clearly related to acorn worms.

Scientific classification: Pogonophores make up the phylum Pogonophora.

Platyhelminthes

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Flatworm, common name for soft-bodied, usually parasitic animals, the simplest of animals possessing heads. They are bilaterally symmetrical and somewhat flattened, and most are elongated. Three main classes are included in the flatworm phylum: tapeworms, which in the adult stage are parasitic in the digestive tracts of animals; flukes, which are parasitic in various parts of different animals; and planarians, which are free-living and nonparasitic. Some authorities include a group of unsegmented marine worms. Other authorities consider them a separate phylum.

The ectoderm (outer surface) of the free-living flatworms is usually covered with cilia; in the parasitic forms the ectoderm usually secretes a hardened material called cuticle. A well-developed musculature, found directly under the epidermis (skin layer), allows the body to expand and contract, thus changing the body shape to a remarkable degree. Vivid pigmentation is sometimes present in the free-living forms, but the parasitic forms are usually unpigmented. Flatworms have no true body cavity; the spaces between the organs are filled with a compact connective tissue called parenchyma. Except in the simplest forms, one end of the body is more specialized for sensory perception, and locomotion takes place in the direction of specialization. The oral and genital openings are on the ventral (under) side. When present, the digestive tract is either saclike or branched and has only one opening. This opening may be equipped with a sucker, as in the flukes, or, as in most planarians, it may have a well-developed pharynx. The nervous system consists of a network with a large ganglion (brain) and various longitudinal nerve cords forming the principal parts. Sensory cilia and “eye spots” may be present in the free-living forms and in the larvae of the parasitic forms. The flatworm has no blood or vascular system. Specialized cells possessing cilia, called flame cells, lead from the interior to one or more openings in the exterior by means of a network of tubes. Together these structures form the excretory system. The reproductive system is highly complex and occupies a large portion of the interior of the animal. Although flatworms are almost all hermaphroditic (both male and female reproductive organs are present in each individual), the eggs and sperm are formed separately. These germ cells either leave the body by separate openings or enter a common chamber, called the genital atrium. Flatworms also are able to reproduce asexually both by binary fission—that is, by pinching themselves apart to become two—and by regeneration, producing an entire new worm from a piece that has been cut off.

Free-living flatworms are found in almost every kind of environment, on land and in fresh and salt water. These forms feed mainly on plankton. The parasitic flatworms often display a complicated life cycle, which may require development in four or five hosts before completion.

Scientific classification: Flatworms constitute the phylum Platyhelminthes. Tapeworms constitute the class Cestoda. Flukes constitute the class Trematoda. Planarians constitute the class Turbellaria.

Phoronida

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Phoronids, common name for a wormlike marine invertebrate animal, a kind of tube worm. There are about 12 species of phoronids. They are sedentary animals that can be as long as 38 cm (15 in). Most species secrete a protective tube in the mud or sand bottoms of shallow seas.

The phoronids are regarded as closely related to the bryozoans and brachiopods because they possess a lophophore, a horseshoe-shaped structure carrying ciliated tentacles (see Tentaculata). The tentacles serve to catch food materials suspended in the water, and the cilia move mucus-entrapped food to the mouth, located at the center of the lophophore. The digestive tract is U-shaped, so the anus is located near the "head" of the animal but outside the lophophore.

The phoronids possess a well-developed circulatory system. Some species are hermaphroditic, in which one individual may have both male and female organs. Fertilization generally occurs outside the body; however, in some species, the eggs develop at the base of the lophophore tentacles.

Scientific classification: Phoronids are members of the phylum Phoronida, of the kingdom Animalia.

Pentastomida

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Tongueworm is any of a group of parasitic, wormlike animals found in the respiratory system of vertebrates, especially reptiles. Tongueworms cling to the lining of the nasal passageways and lungs where they feed on the blood of the host. Also called pentastomids, tongueworms occur worldwide, although most species are tropical.

The body of the tongueworm is highly modified for parasitism, that is, obtaining nourishment from the body of another, usually larger host organism (see Parasite). Adults of most species are 2 to 13 cm (0.8 to 5.1 in) long. Their mouth is jawless and sometimes projects outward as a trunklike proboscis. The mouth is flanked by two pairs of small, fingerlike projections equipped with claws that are used to attach to the host. The name pentastomid, meaning five-mouthed, derives from the fact that, in some species, these four grasping organs resemble the proboscis and look like additional mouths. The single, true mouth leads to a long, straight gut, the front of which forms a muscular pharynx for sucking blood. Frontal glands near the mouth of the tongueworm produce substances that break down the host tissue or prevent the host's blood from clotting. Like most internal parasites, tongueworms have no organs of excretion, gas exchange (breathing), or circulation. The tongueworm's blood flows freely throughout the body cavity. The tongueworm's nervous system consists of a frontal ganglion, or primitive brain, and a ventral nerve cord that runs along the bottom of the body cavity.

The sexes of tongueworms are separate, and the females are larger than the males. Fertilization is internal and occurs within the primary host. The larva has two or three pairs of walking legs, each with two claws. The larva may be autoinfective, that is, it remains in the primary host. If not autoinfective, the larva may form a protective capsule, called a cyst, which either moves through the digestive tract to be deposited with the host's feces or moves passively out of the host's nose or mouth.

Tongueworm eggs may pass out of the host before they hatch. If an intermediate host animal accidentally swallows the cyst or egg, the infective larva emerges inside the new host. It bores through the gut wall and completes its development into the next infective stage. If the intermediate host is eaten by a predator, the predator may acquire the pre-adult tongueworm. The juvenile tongueworm then crawls up the esophagus to the respiratory system and implants itself in the lungs or nasal passageways to complete the cycle. The larvae of one species of tongueworm that infests reindeer can infest the next generation of hosts by boring through the placenta. Examples of typical intermediate hosts and their corresponding primary hosts are cockroaches and lizards, fish and crocodiles, and rabbits and dogs.

Scientific classification: Tongueworms make up the phylum Pentastomida. Their relationship to other animals is not clear; they resemble both arthropods and annelids. One theory on the origin of this group is that they are actually highly modified crustaceans.

Onychophora

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Velvetworm, any of a group of soft-bodied, many-legged, worm-like animals known for their velvety cuticle, or outer covering, and their resemblance to both arthropods (insects, spiders, and crustaceans) and annelids (segmented or true worms). They live in moist tropical and temperate habitats south of the tropic of Cancer. Velvetworms are also known as onychophorans or peripatuses, after the most familiar genus. About 80 species of velvetworms are known.

Mature velvetworms range from 1.5 to 15 cm (0.6 to 5.9 in) in length and may be blue, orange, green, or black in color. Their thin, flexible cuticle, or outer skin, bears many small, scaly, wartlike tubercles and sensory hairs, which produce a velvety appearance. Velvetworms have 14 to 43 pairs of stubby, claw-tipped legs called lobopods. The lobopods contain no muscles. Velvetworms control their body and limb movements with hydrostatic pressure changes within their body cavity. Velvetworms use these pressure changes to lift and lower their legs in waves, as their body creeps along with slug-like motion.

When conditions are too dry or too wet, velvetworms hide in burrows or protected niches until conditions improve. They are nocturnal, appearing only at night, and prey on other small invertebrates. The velvetworm's jaws hold the prey while it is being eaten. Salivary glands produce enzymes that partly digest tissues so the meal can be sucked up. When disturbed or threatened, velvetworms shoot a sticky, quick-hardening slime from two oral papillae, wartlike bumps on either side of the mouth. They can shoot the slime up to 50 cm (19.7 in). The slime is produced by slime glands originating at the base of the oral papillae and may also be used to immobilize prey.

The velvetworm has a pair of fleshy, ringed antennae on its head and a pair of eyes near the bases of the antennae, each with a lens and retina. Blood is circulated by a tube-shaped dorsal heart (located near the top of the body cavity) and flows freely within the body cavity around the internal organs; it carries no oxygen. Gases are exchanged through a system of minute tracheae, or breathing tubes, which open into pits located throughout the cuticle. The pits cannot be closed and are a major source of water loss for the moisture-dependent velvetworm. The velvetworm takes in water by drinking and by absorption through special ballooning sacs on the lobopods. Wastes are excreted from paired sacs called coelomoducts or nephridia, which are present on most body segments and which lead to pores on the legs. The slime glands and female sexual ducts are modified coelomoducts. The brain gives rise to a pair of ventral nerve cords, which run along the bottom of the body cavity and are connected by ladderlike cross nerves.

The sexes are separate in velvetworms; males are generally smaller and may have fewer legs than females. In the species where sexual behavior is known, fertilization occurs through copulation.

Scientific classification: Velvetworms make up the phylum Onychophora. The most familiar species are in the genus Peripatus.

Nematoda

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Roundworm, also nematode, common name for any of a phylum of unsegmented terrestrial, freshwater, or marine worms. Roundworms are almost worldwide in distribution and are abundant in the surface layers of soils. Many of them are economically and medically harmful, living as parasites in plants and animals, including humans. Roundworm infections are common and frequently go unnoticed, but several species cause serious diseases.

Roundworms are cylindrical, tapering animals with simple bodies consisting of an interior gut and a muscular outer wall, separated by a fluid-filled cavity called a pseudocoel (see Animal: Coelom). The outer wall secretes an elastic cuticle that is molted four times during the animal's lifetime. Species range in size from microscopic to about 10 cm (about 4 in) long. Most species have separate sexes, but a few are hermaphroditic; fertilization is internal. The young roundworms, which resemble the adults, develop without metamorphosis.

Although numerous roundworms are free-living, the parasitic forms are of greatest economic interest. One important group, the ascaroid nematodes, includes the threadworms and the common worm of puppies. Another contains the eelworms, which produce root knot of cotton, and forms that produce earcockle of wheat. Other, medically significant forms of roundworm include the various genera known as hookworm; the filaria, which cause elephantiasis; the trichina worm, the cause of trichinosis; and the whipworm, which infests the human intestine.

Scientific classification: Roundworms make up the phylum Nematoda. Threadworms belong to the genus Ascaris. The common worm of puppies is classified as Toxocara canis. Eelworms belong to the genus Heterodera, the forms that produce earcockle of wheat belong to the genus Tylenchus, and the trichina worm belongs to the genus Trichinella. The human whipworm is classified as Trichuris trichiura.

Nematomorpha

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Horsehair Worm, member of a group of long, slender, unsegmented worms that resemble horsehair. The name of their phylum, Nematomorpha, means “threadlike.” Long ago, people thought that these worms were actually hairs from a horse's tail that had come alive. The immature worms, or larvae, are all parasites, feeding within the bodies of leeches and arthropods such as insects and crustaceans. The adults are free-living—that is, they do not depend on a host.

Horsehair worms are 1 to 3 mm (0.04 to 0.12 in) in diameter and up to 1 m (3.3 ft) long. There are two classes of horsehair worms. The first, known as nectonemes, live within the bodies of crabs and their relatives. The adults are planktonic, drifting in the currents of the open ocean. The body has two rows of bristles down each side, which aid in buoyancy. Nectonemes have only one gonad, or sex organ. The second class of horsehair worms is made up of the gordian worms, so named because they appear to tie themselves in knots, much like the complex Gordian knot of Greek mythology. The larvae parasitize leeches and arthropods such as grasshoppers, crickets, beetles, millipedes, and centipedes. The adults occur worldwide in freshwater or moist terrestrial habitats. Gordian worms possess a pair of gonads.

The body of the adult horsehair worm is covered by a relatively thick outer cuticle, or skinlike covering. Underlying the cuticle is a layer of longitudinal muscle running the length of the body. The horsehair worm has no circular muscle, and thus its movement is limited to lashing and curling. The digestive system is simple, even in the free-living adults. There are no excretory, circulatory, or respiratory organs. The larvae probably take up nutrients directly through the body wall during the parasitic phase. Feeding has not been observed in the adults, and most have no mouth, but they grow considerably after they leave the host at the end of the larval stage. It is therefore likely that they do feed by some means. The nervous system consists of a nerve bundle at the head end and a nerve cord running down length of the body. Around the head of some species is a ring of pigmented tissue that may be light-sensitive, but horsehair worms have no eyes. The outer layer of the cuticle is often covered with bumps, some of which may detect touch and some of which produce a lubricant.

Scientific classification: Horsehair worms make up the phylum Nematomorpha. The nectonemes make up the class Nectonematoidea, which has only one genus, Nectonema. The gordians make up the class Gordioidea.

Mollusca

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Mollusk is a common name for members of a phylum of soft-bodied animals (Latin mollus, “soft”), usually with a hard external shell. The mollusks represent a diverse group of marine, freshwater, and terrestrial invertebrates, including such varied forms as snails, chitons, limpets, clams, mussels, oysters, octopuses, squid, cuttlefish, tusk shells, slugs, nudibranchs, and several highly modified deep-sea forms. They all have one anatomical feature in common, the presence of a shell at some stage in the life cycle. Although most mollusks have a shell as adults, the octopus, squid, and deep-sea forms do not. They do however have a small, shell-like structure, called a shell gland, present for a short time during embryonic development. The mollusk phylum is the second largest in the animal kingdom, after the arthropods.

Scientific classification: Mollusks make up the phylum Mollusca. In the class Aplacophora, the body is wormlike. No shell exists, only a tough mantle, and the foot has virtually been lost. The three orders of the class Polyplacophora (chitons) have a series of eight shell plates (valves) in a row and are well adapted to clinging on rocks. The mainly fossil Monoplacophora is now known to have one living genus, Neopilina, discovered in deep water in 1952. The animal has a single flat shell and multiple gills. The class Bivalvia have a shell divided into two valves, and they feed with their gills. As a consequence the head is poorly developed. Members of the class Scaphopoda (tusk shells) have a long, tapered, slightly curved shell and live on sandy bottoms. Members of the class Gastropoda (snails and slugs) are asymmetrical and have only one shell or, as in slugs, are shell-less. The three subclasses of the Gastropoda are the Prosobranchia (mostly marine snails, with three orders), Opisthobranchia (sea slugs and their allies, with eight orders), and Pulmonata (lunged mollusks, largely freshwater and terrestrial, with two orders). The class Cephalopoda are modified by reduction of the foot and shell and the development of arms around the mouth. The two subclasses are Nautiloidea ( Nautilus, with four gills and other archaic traits such as an external shell) and Coleoidea (octopuses, squid, and cuttlefish, with two gills and other advanced traits).

Mesozoa

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Mesozoa (Greek mesos, “middle”; zōion, “animal”), phylum or superphylum of life forms, sometimes thought to be transitional from unicellular to multicellular organisms. The body consists of a layer of outer cells surrounding internal reproductive cells; it contains no real organs. Except at the time of dispersal, mesozoans live as internal parasites of marine invertebrates. Some authorities consider them degenerate flatworms; others deny that they are animals. The group contains about 50 species placed in two classes or orders.

Loricifera

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Loriciferan, name of a group of tiny marine animals, first identified in 1974, and established as a new phylum in 1983 by Danish zoologist Reinhardt Kristensen. Loriciferans are unusual, nearly microscopic creatures 0.25 to 0.33 mm (0.01 to 0.013 in) long. They are generally oval in shape. The head ends in a beaklike conical mouth that can be retracted into the body. The mouth is surrounded by nine rings of bristly scales, the first set of which point forward, the rest backward. The body is encased in several hard plates that resemble a corset, from which the group gets the name Loricifera, meaning “corset-bearer.” At the hind end of the body is an anus. Much of the body cavity of adults is filled with either developing eggs or testes. There is a specialized immature form known as a Higgins larva. It has a pair of oarlike scales, called toes, at its hind end which are used for locomotion. Little is known about the reproduction and life history of loriciferans.

Scientific classification: Loriciferans make up the phylum Loricifera. The first discovered loriciferan is classified as Pliciloricus enigmatus.

Cycliophora

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Symbion, a tiny marine organism so different from any other that it has given rise to a new phylum (see Classification). Symbion (meaning “living with”) is a commensal, a harmless companion that lives on the mouth hairs of the Norwegian lobster and feeds on the scraps the lobster leaves behind after its messy meals. Symbion's distribution is unknown but may coincide with that of its lobster host.

Symbion takes on different forms throughout its strange life cycle. The most common form is the feeding stage, which is about 0.1 mm (0.004 in) long. The body is urn shaped and attached to the lobster by a short stalk and an adhesive disk. On the other end is a funnel-like mouth topped with a ring of microscopic hairs, or cilia. The mouth leads to an S-shaped esophagus, or throat, and a U-shaped digestive system. The first part of the U forms a stomach lined with ciliated and secretory cells; farther along it becomes an intestine, also lined with cilia. Because of the U shape of the digestive system, the anus, or excretory opening, is near the mouth. The two-lobed brain is situated between the funnel base and the anus. The outer surface of the animal is layered and sculptured with pentagonal shapes. Symbion replaces its mouthparts and nervous system several times during its life by forming an internal bud consisting of a new digestive tract and brain. As this bud matures, it eventually replaces the old structures.

The reproductive cycle is unusual and complicated and is an important reason for putting Symbion in its own phylum. Symbion reproduces in two different phases: asexual budding and sexual fertilization. In the asexual phase, the feeding stage forms an internal bud containing an embryo that develops without fertilization into a Pandora larva, a type of free-swimming larva. The Pandora larva escapes and settles on the same lobster host, developing into another feeding stage.

Symbion's discovery was announced by the Danish scientists Peter Funch and Reinhardt Mobjerg Kristensen in 1995. They documented its curious life cycle and provided evidence to distinguish it from other species to which it may be related, such as rotifers, moss animals, and entoprocts, small marine and freshwater animals that Symbion resembles.

Scientific classification:Symbion pandora is the sole member of the phylum Cycliophora, or “wheelmouth” animals. It is also the only member of the family Symbiidae, order Symbiida, and class Eucycliophora.

Hemichordata

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Acorn Worm, common name for simple, wormlike marine animals in the hemichordate phylum. They are of special interest because of their close relationship to chordates. This connection is evident in the adult anatomy. Some representative acorn worms have gill slits, traces of a supporting structure resembling a notochord, and a tubular nerve cord, which are features characteristic of vertebrates. The larval stages of acorn worms, however, are very much like those of echinoderms such as starfish, indicating a remote common ancestry of echinoderms and vertebrates.

The hemichordates are divided into two classes comprising about 50 species. The first class, the acorn worms, consists of animals that average 10 cm (4 in) in length, although some species may be up to 1.5 m (up to 5 ft) long. They construct burrows, commonly U-shaped, in sand of shallow seafloors using an extendable, muscular proboscis attached to a thick collar that resembles an acorn—hence the name. They secrete a slime that collects food particles on the proboscis and collar, but some species filter sediments and sand through a complicated pharynx with many gill slits. The second class consists of small, usually colonial animals of the deep sea. They are not worm-shaped but stout, and they usually construct tubes. Food is captured by tentacles that project from the tube. The body is much simplified, and gill slits are reduced to one pair or none.

See also Balanoglossus.

Scientific classification: Acorn worms make up the class Enteropneusta in the phylum Hemichordata. The other class of hemichordates is Pterobranchia.

Gnathostomulida

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Gnathostomulid, group of microscopic marine worms that live between grains of sand in shallow ocean water. These invertebrates are able to live for long periods without oxygen (see Anaerobe) and are common in stagnant bottom muck and black sand. More than 80 species of gnathostomulids have been described.

Gnathostomulids resemble flatworms and were once classified in the same phylum. Like flatworms, gnathostomulids are bilaterally symmetrical (both sides of the body are identical along the midline) and have waving body cilia (tiny hairlike projections); they lack an anus and a coelom (internal body cavity) and are hermaphroditic (individuals have both male and female sex organs). Unlike flatworms, however, each epithelial (skin) cell in gnathostomulids has only one hairlike cilium. In addition there are significant differences in sperm structure between gnathostomulids and flatworms.

Gnathostomulids are generally 0.5 to 1.0 mm (0.02 to 0.04 in) in length with a slight constriction of the body separating the head from the trunk. They move their long transparent bodies with the propelling force of their rotating cilia. Unlike flatworms, they have the ability to reverse the direction of the ciliary beat. The contractions of three or four pairs of longitudinal muscle fibers also contribute to movement. Gnathostomulids have a mouth located on the underside of the body behind the head. They graze on bacteria and fungi using a pair of toothed jaws that grasp and push food into the intestinal sac.

Even though gnathostomulids possess both male and female sex organs, they cannot fertilize themselves. Eggs are fertilized when one gnathostomulid injects a packet of sperm into another individual’s body using a penislike organ that is equipped with a piercing tip in some species. A single large egg is released by breaking through the body wall and develops without larval stages into an adult. The parent worm regenerates rapidly after releasing the egg. Some gnathostomulids appear to alternate between a nonsexual feeding phase and a sexual phase during which they do not feed.

Scientific classification: Gnathostomulids make up the phylum Gnathostomulida, and are members of the superphylum Aschelminthes.

Gastrotricha

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Gastrotrich, group of microscopic wormlike animals that are common in aquatic environments worldwide. The gastrotrich lives in bottom sediments and on the surface of submerged vegetation and debris. Its head is divided into lobes and its body is generally flat, transparent, and unsegmented. Its back and sides are spiny, bristly, or scaly. The flattened bottom surface bears small hairs, or cilia, in characteristic patterns that are helpful in classifying species. Along the sides of the body are adhesive tubes that are used for clinging to vegetation.

Gastrotrichs range in length from 0.05 to 4.0 mm (0.002 to 0.16 in). Marine gastrotrichs, those living in the ocean, are abundant on the surfaces of corals and in shallow sandy areas, while freshwater species prefer standing water such as puddles, marshes, and wet bogs. They may be present in habitats where there is much decay and they can withstand low levels of dissolved oxygen for short periods. The gastrotrich feeds as it moves, ingesting bacteria, algae, small protozoans, and organic debris from the substrate. Waving cilia on the head create currents that push food particles to the mouth.

Marine gastrotrichs are hermaphroditic (having both male and female sex organs) and individuals alternately produce eggs and sperm. Most freshwater species are entirely female and reproduce through parthenogenesis (egg development without fertilization). A female will produce one to five very large eggs in its lifetime. The eggs are of two types: thin-walled eggs that develop as soon as they are laid, and thick-walled eggs that require exposure to harsh conditions such as drying, freezing, or high temperatures before they develop. Gastrotrichs have no larval stages. On emergence from the egg, the gastrotrich is already about 25 percent of its adult size. It grows rapidly and some species reach sexual maturity in only three days. The lifespans of gastrotrichs in nature are unknown, but individuals in laboratory cultures live 3 to 22 days. Gastrotrichs are important as food for many organisms in aquatic food webs.

Scientific classification: Gastrotrichs make up the phylum Gastrotricha, which contains two orders. Animals in the order Macrodasyida are strictly marine, and those in the order Chaetonotida are primarily freshwater.

Entoprocta

2008-09-10T03:53:00.005-07:00

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Entoprocts, tiny, mosslike invertebrate animals found in shallow waters. Entoprocts have tentacles and oval-shaped bodies, and usually live in branching colonies. Entoprocts lack a true coelom, or body cavity. A slender stalk attaches the body mass, or calyx, to either an inanimate object or another animal. The digestive tract is U-shaped. On the uppermost surface of the calyx are tentacles made of cilia arranged in a circle around the mouth and anus. The movements of the hairlike cilia create currents that sweep tiny animals and suspended particles into the mouth.

Entoprocts may live singly but are more often found as colonial groups, with many individuals arising from a single animal through the asexual process of budding. When sexual reproduction occurs, large yolky eggs are brooded in a special cavity within the circle of tentacles. With the exception of one freshwater genus, the entoprocts are exclusively marine. Because of their small size they are difficult to observe without the aid of a microscope.

Scientific classification: Entoprocts make up the phylum Entoprocta.

Ectoprocta

2008-09-10T03:53:00.003-07:00

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Moss Animals, common name for two phyla of small, simple aquatic animals that feed with a crown of tentacles called a lophophore and usually form attached, mossy colonies. The classification of these two phyla has varied to reflect changing opinions about the relationship of moss animals to other phyla. Authorities who think the two groups have a close common ancestor retain the phylum name Bryozoa for all moss animals and treat endoprocts and ectoprocts as classes. Others use the term Bryozoa only for ectoprocts, and still others think that ectoprocts are related to the Tentaculata and endoprocts to the Aschelminthes.

Endoprocts, which are marine except for one freshwater species, have a globular body that is mounted on a stalk. The lophophore surrounds both mouth and anus. The animals reproduce both sexually and asexually, often forming colonies of connected individuals by the latter process. In ectoprocts, which are primarily marine, the lophophore does not surround the anus. The colonies that ectoprocts form by asexual reproduction are of varied structure, and each member usually has a hard, protective coating.

Scientific classification: Endoprocts make up the division Endoprocta, or Entoprocta. Ectoprocts make up the phylum Ectoprocta, or Bryozoa.

Echiura

2008-09-10T03:53:00.001-07:00

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Spoonworm, common name for any of a small phylum of unsegmented worms with an internal body cavity and characterized by a stout body, or trunk, and a long flexible, spoon-shaped proboscis, or feeding organ. They are found on the ocean bottom from the shallow intertidal zone to depths of 10,000 m (32,808 ft.)

Mature spoonworms, also called echiurans, are sedentary bottom feeders that burrow in mud, sand, or debris. A few live in rock crevices or enclosures such as abandoned sand dollar shells. Most spoonworms are dull in color, but a few are green, red, or transparent. With the proboscis retracted, they range in length from 1 to 20 cm (0.4 to 7.9 in). In most species, the trunk of the spoonworm lies buried in the muck or debris on the ocean bottom while the proboscis extends outward to grope for food. The touch- and taste-sensitive proboscis is flexible and may extend up to 2 m (6.56 ft). It has a groove lined with cilia (tiny hairs) along its length. Glands on the proboscis secrete sticky mucus that picks up the debris on which the spoonworm feeds. The cilia in the groove wave to transport mucus and debris to the mouth. The skin of the spoonworm is rich with sensory cells and mucous glands. Three layers of muscle line the interior of the body cavity, or coelom. The spoonworm moves by exerting pressure with these muscles on the coelomic fluid.

Spoonworms have a three-part digestive system consisting of a foregut, a stomach, and a long, coiled midgut, in which most digestion takes place. The circulatory system is very simple, consisting of two vessels that run the length of the body cavity and does not include a heart. A ventral nerve cord along the underside of the body cavity and a ring of nervous tissue near the head comprise most of the spoonworm's nervous system. Spoonworms breathe by diffusion of oxygen through the skin. All spoonworms have a pair of funnel organs, pocket-like sacs with openings on the underside of the animal.

The sexes are separate in spoonworms and fertilization occurs externally in most species. Gametes, or sex cells, are produced in sex organs near the ventral nerve cord. Sperm or eggs usually exit the body through the funnel organs. In some species the eggs are retained and the organs function as a uterus. The larvae, classified as trochophores, are similar to those of polychaetes, or segmented worms, and in most species of spoonworm, they float freely in the ocean for several months before settling as adults. In some spoonworms, males and females are very different and sex is determined by an unusual mechanism. In the green bonellid, if the larva settles away from others of its species, it becomes a female, up to 8 cm (3.15 in) long. If, however, it lands on or near the proboscis of a female of the same species, the larva will become a male, due to a hormone produced by the female's proboscis. The tiny males are only 2 to 3 mm (0.08 to 0.12 in) long and live on the female's body or internally in one of her funnel organs.

Scientific classification: The spoonworms comprise the phylum Echiura. The green bonellid is Bonellia viridis. The innkeeper is Urechis caupo.

Echinodermata

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Echinoderm, common name for about 6000 living species constituting a phylum of marine animals, such as starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers. They usually show a superficial five-part radial symmetry, and generally are equipped with peculiar tube feet. The phylum name is derived from the spiny skin.

An echinoderm such as the starfish typically has a mouth surrounded by five arms that bear minute, fleshy tube feet with which the animal clings and crawls. The tube feet are supported by a complex internal hydraulic system that is inflated with seawater. Some echinoderms, especially brittle stars, crawl or swim by moving their arms. Often, as in sea urchins, rows of tube feet extend along the body surface, and arms are absent. The spines are particularly well developed in sea urchins. The skeleton, made up of calcium carbonate, may form a large proportion of the body, or, as in some sea cucumbers, it may be greatly reduced. The fossil record shows that the five-rayed pattern is a late evolutionary acquisition, and deviations from it are common. The animals have a well-developed gut, but the nervous and circulatory systems are simple. Echinoderms are slow-moving and without complex behavior patterns.

Echinoderms are common on the ocean bottom at all depths; in the deep sea they often make up the bulk of living material. They may be grazers (most sea urchins), feeders on small particles (many brittle stars), or predators (most starfish). Starfish and a few others are pests, as when found in oyster beds. Sea cucumbers and sea urchins are eaten by humans.

Scientific classification: Echinoderms make up the phylum Echinodermata. The living echinoderms are commonly divided into two subphyla. The stalked or attached Pelmatozoa consist of the single class Crinoidea, or sea lilies and feather stars, with 650 species. The free-living Eleutherozoa consist of the classes Holothuroidae, or sea cucumbers, with 900 species; Echinoidea, or sea urchins and sand dollars, with 850 species; Asteroidea, or starfish, with about 1500 species; and Ophiuroidea, or brittle stars, with about 2000 species. Many authorities, however, unite Asteroidea and Ophiuroidea into a single class, Asterozoa (or Stelleroidea). About 20 extinct classes are found in the fossil record.

Pictures of Invertebrates

2008-09-09T20:33:00.000-07:00

Gooseneck Barnacles
Gooseneck barnacles are crustaceans that live in the intertidal zones of temperate and cold water oceans, particularly in areas of heavy surf. The hard-shelled portion of the gooseneck barnacle’s body, which contains the internal organs, is supported on a long muscular stalk. Gooseneck barnacles use this stalk to latch onto floating objects or rocks, where they cluster in dense groups.

Gray Snakelocks Anemone
The gray snakelocks anemone, sometimes called the pink-tip, is related to the jellyfish, corals, and hydroids. Although sea anemones can move, they do not actively pursue prey but rather capture fish, shrimp, or other invertebrates that swim past or fall on them from above. The sea anemone’s color results from the presence of a symbiotic algae, called zooxanthellae, living in the anemone’s body tissues.

Great Gray Slug
All species of marine and terrestrial slugs are shelless mollusks. Terrestrial slugs, such as the great gray slug, generally feed on leaves and can cause considerable damage to trees and cultivated plants in gardens and greenhouses.

Green Hydra
The green hydra is the freshwater counterpart of the sea anemone, belonging to the same phylum as the sea anemone, coral, and jellyfish. Possessing six to ten tiny tentacles armed with potent stinging cells, the hydra captures small organisms from the surrounding water. It is often found in colonies of many individuals. The hydra is capable of regenerating lost body parts, even in cases where the injury has been extensive.

Hermit Crab
Hermit crabs are distinguished from other crabs by the lack of a shell on the abdomen. As a result, hermit crabs must find empty snail shells to temporarily inhabit. While walking or feeding, hermit crabs extend their antennae, claws, and two pairs of walking legs out of the shell opening. When threatened by predators, hermit crabs quickly withdraw their bodies back into the protection of the shell. The large claw, the last part of the body to be withdrawn, often acts as a door, closing off the interior of the shell from predators. As hermit crabs grow, they must continually find new, larger shells in which to live.

Human Head Louse
The human head louse, Pediculus humanus, is one of several kinds of lice with mouthparts specialized for sucking blood. The small, wingless insect has a flattened body about 3 mm long, with a claw on the end of each leg that helps it cling to the hair of its host. Females lay whitish eggs, called nits, once a day, attaching them to the hair with a sticky substance until they hatch in about a week. Head lice are unpleasant and undiscriminating guests. They infest people who bathe often as well as those who do not, leaving itchy red spots on their hosts’ scalps.

Millipede
The millipede is a segmented arthropod found in damp, moist habitats worldwide. The body of the millipede may have from 9 to over 100 individual segments, each of which bears a pair of legs. Millipedes feed on decaying vegetation and are generally harmless. When threatened or handled, they curl up in a tight ball. For defense against insect predators, millipedes rely on their stink glands, which secrete a noxious chemical substance that repels predators.

Murray River Crayfish
Although identical in shape to the marine lobster, the freshwater crayfish is more adaptable, being able to live in freshwater streams, ponds, and even terrestrial burrows. In some agricultural areas of Spain, crayfish are so abundant they are considered pests.

Portuguese Man-of-War
The Portuguese man-of-war is actually a colony of specialized polyps that all contribute to the well being of the colony by performing specific tasks, such as feeding or providing buoyancy control. The man-of-war has a relatively large, gas-filled bladder that provides flotation for the entire colony. A large collection of feeding polyps suspended from the underside of the float, each with a single, long tentacle, captures and digests food, which is then shared with the entire colony by means of interconnecting digestive cavities. Although the Portuguese man-of-war resembles a jellyfish, it belongs to Class Hydrozoa in the phylum Cnidaria, while true jellyfish belong to Class Scyphozoa in the same phylum.

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Pictures of Invertebrates

2008-09-09T20:28:00.000-07:00

Black Widow Spider
The female black widow spider, distinguished by the red hourglass marking on the underside of her abdomen, is probably the best known and most feared of all North American spiders. In spite of the female black widow’s small size of 1.2 cm (0.5 in.), its venom is quite toxic and may cause a wide range of symptoms in humans, including pain, swelling, nausea, and sometimes death. The male of this species is harmless to humans and lacks the hourglass marking on the abdomen.

Blue Spotted Sea Urchin
This underside view of the blue spotted sea urchin shows its mouth apparatus, commonly called Aristotle’s lantern. This structure is composed of five jaws arranged in a radial, or concentric, pattern. This arrangement allows the sea urchin to feed efficiently on a variety of marine algae and kelps.

Branching Coral Colonies
Branching coral is actually a colony of very small individual animals called coral polyps. Branching corals are considered hard corals, since they have a hard calcium carbonate skeleton. Their bright colors result from the presence of symbiotic algae that live in their body tissues and produce most of the food that the coral needs to survive.

Chambered Nautilus
A cutaway view of the shell of the chambered nautilus reveals the compartments that housed the nautilus when it was smaller. These smaller chambers, now connected together by a small calcified tube, regulate the buoyancy of the nautilus as it swims along. The compartments are filled with nitrogen gas, which is produced by the nautilus.

Clams
Clams have long been one of the most popular of the edible shellfish. Referred to as bivalve mollusks because of the two valves, or shells, that enclose the body, these small filter-feeding animals are commonly found in intertidal areas throughout the world. Strong internal muscles, a hinge ligament, and a calcified hinge at the apex of the shell allow the clam to protect itself against many types of predators by keeping the shell tightly closed. The prominent growth rings found on the outer surface of the clam shell are useful in determining the clam’s age.

Common Cuttlefish
Related to the octopus and squid, the common cuttlefish is an open water species of cephalopod mollusk that swims by undulating a continuous fin along the length of its short, fat body. The cuttlefish is commercially important throughout many parts of its range. A supporting rod of calcium carbonate present within the cuttlefish, called cuttlebone, is used commercially as a polishing agent and as a source of calcium and salts for captive birds and other animals.

Common Octopus
The common octopus has the typical octopus body form consisting of three main regions: the mantle, limbs, and head. The mantle, a large, muscular, bulbous sac, contains most of the internal organs, including the gills, digestive tract, ink sac, and reproductive organs. The limbs consist of eight arms. Along the length of each arm is a double row of suckers equipped with tactile and olfactory receptors.

Earthworm
Earthworms have a segmented, compartmentalized, cylindrical body and range in length from several centimeters (a few inches) to nearly 3.3 m (11 ft). They have no eyes, ears, or lungs. Earthworms breathe when air that is present between soil particles diffuses through their thin skins, and they are forced to the surface if these air pockets fill with rainwater. When a worm moves, it uses its longitudinal muscles to extend the front of its body into the soil ahead of it, pulling the back part up behind it. Setae, tiny projections from each segment of the worm, stick into the surrounding soil to keep the worm from slipping. The digging action of earthworms helps to aerate and mix the soil. Earthworms actually consume some of the soil as they dig, and their fecal deposits, called castings, also help enrich the soil.

Echinoderms
Members of the phylum Echinodermata, commonly called echinoderms, or spiny-skinned animals, are so named because of their spiny outer body coverings. Echinoderms differ from other animals in that they have a water vascular system that uses seawater to accomplish respiration, locomotion, and reproduction. The echinoderms include marine groups such as the sea stars (top, left), sea cucumbers (bottom, left), brittle or serpent stars (top, center), sand dollars (bottom, center), sea lilies (right), sea urchins, basket stars, heart urchins, and feather stars.

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Pictures of Insects

2008-09-09T20:25:00.000-07:00

Luna Moth
The full-grown luna moth has transparent circles bordered by light yellow and blue rings on its light green wings. Luna moths reproduce twice a year and eat the leaves of trees in the deciduous forests they inhabit. Now endangered because of contaminated food sources and pesticides, the luna moth is found only in North America.

Peacock Butterfly
The conspicuous eyespot markings of the peacock butterfly, Inachis io, make the insect unmistakable. The butterfly uses its patterning in self-defense, opening its wings if threatened by a bird and attempting to alarm the attacker by turning the pattern towards it. The butterfly also rubs its wings together to make a noise that helps scare off predators.

Praying Mantis
The praying mantis is so named for the prayerlike posture it assumes while waiting for its prey. Although the praying mantis generally eats insects and small tree frogs, the female will devour part of her own mate. Commonly found in tropical and warm temperate climates, the mantis was introduced into the United States to help control certain insect populations.

True Locust
The true locust is one of over 5000 species of grasshopper in the family Acrididae. Locusts travel in huge numbers capable of feeding on and destroying entire fields of cultivated plants and any nearby vegetation. Approaching swarms create an ominous hum and sometimes are large enough to block out sunlight.

Tumblebug
The tumblebug is one of 30,000 species of scarab beetles, which include dung beetles and chafer beetles. The tumblebug forages on decaying plant material and lays its eggs in small balls of dung, which then serve as a food source for the emerging larvae.

Walkingstick
Walkingsticks have the colors and shapes of the plants on which they live, resembling twigs, or dried leaves. The eggs of many species resemble seeds. Walkingsticks are vegetarians, feeding on leaves. Shown here is Extatosoma tiaratum, an Australian species resembling a spiny, leafy twig.

Worker Honey
As they fly from flower to flower, worker honey bees collect pollen grains and pack them onto their hind legs in special hair-fringed pockets known as pollen baskets (shown here holding a glob of yellow pollen on the hind leg). Nectar, the sweet liquid produced by flowers, is sucked into the honey stomach, an internal storage sac. In the hive, field bees deposit their pollen pellets into empty storage cells of the comb and regurgitate nectar to waiting hive bees. The hive bees mix some nectar with the pollen to make bee bread, a spoilage-proof larval food, and gradually concentrate the rest of the nectar into honey by dehydration.

Pictures of Insects

2008-09-09T20:22:00.000-07:00

American Cockroach
The American cockroach is one of the hardiest species of cockroaches. Unlike most other cockroach species, the American cockroach can fly and is also attracted to light.

Aphids
Aphids are small insects found throughout temperate regions of the world. They parasitize a variety of wild and commercially important plants by sucking out plant fluids. Because aphids exude a sweet, sticky fluid that can be used by certain species of ants, herds of aphids are often found guarded and tended by ants.

Blue Damselfly
After mating, blue damselflies deposit their eggs in water. The eggs hatch and develop into an aquatic larval form, which eventually leaves the water, undergoes metamorphosis, and changes into an adult.

Caterpillar
The larva of a butterfly or moth, known as a caterpillar, has a plump cylindrical body and chewing mouthparts. Most caterpillars eat leaves or other parts of plants and grow rapidly, shedding their skin several times as they grow. The caterpillar of a death’s head hawkmoth, Acherontia atropos, is pictured here.

Firefly
The firefly, belonging to the family Lampyridae, is one of a number of bioluminescent insects capable of producing a chemically created, cold light. Both males and females can generate the light, which is believed to attract them to each other. The light is produced when two chemical substances created by the firefly, luciferin and luciferase, come into contact with oxygen.

Forager Ant
A forager ant searches for food among blades of grass in South Africa’s Karoo National Park.

Fruit Fly Laying Egg
The small vinegar flies of the family Drosophilidae, commonly called fruit flies, have been exceptionally useful in scientific research. Their short reproductive cycle (a new generation of adults develops in only two weeks) and uncomplicated genetics make them ideal subjects for studies of heredity. This fly lays its eggs in rotting fruit and therefore does not need the stiff, sharp ovipositor that other fruit flies use to drill into fruits and stems.

Great Diving Beetle
The great diving beetle has adapted to an aquatic environment. A voracious predator, the diving beetle feeds on tadpoles, small fish, and other insects and their larvae. Not strictly limited to the aquatic environment, diving beetles are capable of flying from one pool to another.

Hornet
The European hornet is the wasp Vespa crabro, common on the east coast of the United States, where it is also called the giant hornet. This wasp, introduced from Europe in the mid-1800s, constructs its nest of hexagonal cells inside hollow trees. Wasp nests are paper, made of partially digested wood and plant fiber. Hornets may emerge from their nests at night and cluster around sources of light. Like other wasps, hornets have a painful sting.

Katydid
The katydid gets its name from the characteristic sound made by males as they rub their wings together to attract females. It is a tree-dwelling insect in the grasshopper family. The katydid resembles a folded green leaf in both color and appearance and uses this mimicry to escape detection from predators. Pictured here is an insect of the scudderia species.

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Pictures of Fishes

2008-09-09T20:16:00.000-07:00

Ratfish
The ratfish is a member of a species of deep-water fish related to sharks. The ratfish is characterized by a long tail and a poisonous spine in front of the dorsal fin.

Rosy Barbel
This fish of the genus Barbus, known as the rosy barbel, swims in a clear freshwater stream amidst the aquatic plants and roots on which it feeds. Part of the carp family, barbels live at the bottom of rivers or streams during the day and use their whiskerlike feelers, called barbels, to find food at dusk. Several species of barbels exist in western Asia and central and southern Europe, where the fish is prized in sports fishing.

Sawfish
Although sharklike in appearance, sawfish are actually a type of ray and are distinguished by the presence of gill openings on the lower surface of the head rather than on the sides of the head as in sharks. The sawfish snout is elongated into a broad, flat sword with opposing rows of large teeth. When feeding, the sawfish thrashes the saw from side to side, wounding and killing small fish. Sawfish are common in the shallow coastal waters of tropical seas and can ascend moderate distances up freshwater rivers.

Sea Horse
The Hippocampus hudonius, also known as the common sea horse, is the largest of over 24 species of sea horses. Sea horses swim fastest in the horizontal position, but can also propel themselves while remaining vertical. Sea horses, like pipefish, have unusual breeding habits. Following mating, a female sea horse deposits her eggs in a brood pouch located on the abdomen of the male sea horse, who then takes care of the eggs until they hatch.

Skipjack Tuna
Skipjack, small, fast-swimming tuna, are distinguished by the dark, horizontal lines found on their streamlined, torpedo-shaped bodies.

Spiny Puffer
The spiny puffer, or burrfish, has a unique defensive mechanism that protects it from predators. When threatened, the spiny puffer inflates its body with water or air, which causes the numerous long spines covering the body to be erected. The inflated body and the sharp spines make it difficult for a predator to ingest the puffer. After the danger has passed, the puffer slowly deflates itself and resumes a more normal shape.

Squirrelfish
Squirrelfish are found in coral reefs throughout the tropics. They are predators, primarily eating small invertebrates such as worms, snails, and shrimp. Squirrelfish are nocturnal; at night their large eyes help them see and their reddish color helps to camouflage them from predators. During the day, they hide in crevices or caves.

Tilapia
Fishes of the genus Tilapia are popular as both aquarium and food fishes. Some species of tilapia are mouth brooders, protecting unhatched eggs and newly hatched young by carrying the eggs and young in their mouths. Usually the female carries the offspring, but in a few species the male also participates in mouth brooding.

White Mullet
The white mullet, commonly found in coastal marine waters and estuaries in temperate and tropical North and Central America, is one of approximately 95 species of mullets found worldwide. White mullets filter plankton and fine particles of organic material from the water and bottom sediments with their fine, sievelike gill rakers.

Winter Flounder
The winter flounder belongs to a group of marine fish known as flatfish. Its flattened body, with both eyes on the same side of the head, and ability to change its body coloration to match that of the immediate background make the winter flounder well adapted for a bottom-dwelling existence.

Pictures of Fishes

2008-09-09T20:12:00.000-07:00

Great White Shark
The great white shark, largest of the strictly carnivorous sharks, is found in tropical and temperate oceans and seas worldwide. Great white sharks use hearing, smell, sight, taste, touch, and electrical perception to locate food.

Hammerhead Shark
The hammerhead shark, distinguished by the lateral expansion of the head into a hammer-shaped structure, is perhaps the most easily recognized shark. The great hammerhead roams tropical and subtropical seas feeding on stingrays, bony fish, and invertebrates. In this photo the hammerhead’s eye is visible at the tip of the hammer-shaped head structure.

Hi-Hat Drumfish
This drumfish’s vivid black and white stripes, while popular with aquarium owners, do little to attract other drumfish. Instead, potential mates swimming out of visible range detect the fish’s far-reaching “knocking” and “drumming” noises, vibrations produced by tightening the muscles of the swim bladder. This tropical Atlantic species gets its name from its tall dorsal fin.

Malawi Blue Cichlid
The Malawi blue cichlid is found in Lake Malawi (also called Lake Nyasa) in eastern Africa. It engages in an elaborate courtship and afterwards provides extensive care for the developing eggs and newly hatched fry. The Malawi blue cichlid, along with dozens of other species of brilliantly colored cichlids from the great lakes of eastern Africa, is prized as an aquarium fish.

Minnow Family
The dace (top) and the chub (bottom) are members of the minnow family. Ranging across North America and Eurasia, the minnow family represents the most important group of freshwater forage fish. All minnows lack teeth in the upper and lower jaws. When a minnow is eaten or injured by a predator, the fish releases a substance into the water, warning other minnows of the danger.

Mosaic Moray Eel
Moray eels inhabit tropical seas where they stalk prey from hidden spots, such as holes in coral reefs. Their cavernous mouths, powerful jaws, and needle-sharp teeth enable eels to capture and eat their prey, mainly other fish and mollusks.

Mudskipper
The fish known as the mudskipper can propel itself over land by moving its pectoral fins. Mudskippers can remain out of water for several days by breathing air trapped in highly vascularized cavities in the mouth and gill chambers. They use this special ability to feed on the rich supply of crustaceans present in the mud of mangrove swamps and estuaries. Mudskippers inhabit the tropical coastal regions in the Indian and Pacific oceans.

Pacific Hagfish
The Pacific hagfish belongs to a group of fish known as the agnathans, considered the most primitive of the living fish. The hagfish, which is blind, lacks true jaws and instead has a sucking disc capable of attaching to the sides of larger fishes. Following attachment, the hagfish drills a small hole into the side of the host fish with its tongue and draws out the body fluids and blood. The hagfish also lacks scales and a sympathetic nervous system.

Panther Grouper
The panther grouper, so named because of its spotted appearance, is a member of the grouper family. This fish has a remarkably large mouth cavity and is able to eat sizeable prey, including fish and invertebrates. Although the color pattern seems quite conspicuous against a light-colored background, it makes the panther grouper inconspicuous against the vibrant background of the coral reef.

Piranha
There are at least two dozen species of South American tropical rain forest fish that are grouped together under the name of piranha. Ranging in size from under 15 cm (6 in) to nearly 60 cm (24 in), the piranha is perhaps the most feared of all fish in the rain forest due to the razor-sharp teeth along the leading edge of both jaws. Although some species are strictly carnivorous, not all are considered dangerous to man.

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Pictures of Fishes

2008-09-09T20:08:00.000-07:00

African Lungfish
The African lungfish is one of three species of lungfish. This lungfish is equipped with both a lung and rudimentary gills. During the dry season, the African lungfish is able to survive by curling itself into a tight ball with its tail covering the eyes. Mud adheres to the body mucous, forming an impervious casing. The lungfish then becomes dormant, or estivates, until the rainy season again fills the pool, softens the mud casing, and releases the fish.

Betta
The betta, or Siamese fighting fish, is native to Southeast Asia. It has been extensively cultured for the aquarium trade. Cultured bettas have long, flowing fins and brilliant colors. They must periodically swim to the surface to capture air in a specialized structure called a labyrinth organ. By breathing atmospheric oxygen, bettas are able to inhabit oxygen-poor waters where few other fish can survive.

Bicolor Parrot Fish
Parrot fish have the unusual ability to change gender. This female bicolor parrot fish may have been a male in the past, or may transform into a male soon. Parrot fish use their strong jaws to break off small pieces of coral and graze on algae growing among the coral.

Brown Bullhead
Valued for food and sport, the brown bullhead, a North American species of catfish, lives in many freshwater streams in the eastern United States. Usually measuring less than 46 cm (18 in) long, the brown bullhead exhibits the typical whiskerlike feelers that give the catfish its name. The brown bullhead is considered the most commercially important of all catfish.

Butterfly Fish
The butterfly fish is a member of the order Perciformes, the largest order of bony fishes. Hundreds of species of butterfly fish are found on coral reefs around the world. Fast and flexible, they can dart quickly into coral crevices to avoid predators and chase after food items. Most species of butterfly fish are brightly colored and patterned, with one or more false eyespots on the fins. This type of coloration serves to disrupt the outline of the body against the background of the coral reef, making it difficult for predators to detect them.

Chain Moray
The chain moray, a coral reef dweller, is a member of the eel family, fish that occasionally lack fins and whose gill openings are reduced to small circular openings. Secretive by nature, the chain morays usually inhabit a coral cave or crevice and wait for unsuspecting fish and invertebrates, which they capture with their sharp teeth and powerful jaws.

Common Sunfish
The common sunfish, a close relative of the bluegill sunfish, largemouth bass, and smallmouth bass, is a small, spiny-rayed, freshwater fish with a bright orange tip at the end of its gill flap. Native to drainage basins east of the Rocky Mountains, this sunfish is popular with young anglers.

Cookie-Cutter Shark
The cookie-cutter shark is named for the cookie-shaped bites that it takes out of its prey. Using special lips modified for sucking and a movable tongue that retracts to form suction, the cookie-cutter attaches itself to the side of prey. It then presses its sharp teeth into the prey’s flesh and uses a twisting motion to cut and remove a round plug of flesh. Even though the cookie-cutter is one of the smallest species of sharks, it preys on large animals such as whales, dolphins, and sharks, and has even bitten into submarines.

Domestic Goldfish
The numerous varieties of domestic goldfish have all come from the wild goldfish of eastern Asia. Domestic goldfish have been bred for centuries, especially in Japan and China, and have adapted to fresh waters around the world. Goldfish can be extremely long-lived and have become popular as domestic pets.

French Angelfish
The French angelfish is a common inhabitant of the coral reef community. The angelfish is easily identified by its large dorsal and anal fins and the prominent vertical yellow stripes along the sides of its body.

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Pictures of Amphibians

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Broken-Striped Newt
The adult broken-striped newt is found in ponds, pools, and quiet streams in low-lying coastal areas of North and South Carolina. Growing to a maximum size of 9.5 cm (3.75 in), this newt feeds on insects, leeches, small amphibians, worms, small crustaceans, and frog eggs.

Burrowing Frog
This frog’s short, powerful legs are well built for digging. It burrows into the cooler soil of its South Australian desert habitat to wait out the unpleasantness of extreme heat, descending to a state of torpor much like hibernation. Other kinds of frogs burrow to conceal themselves or to ambush prey. Many have sharp snouts or flattened spadelike toes that aid them in their digging.

Caecilian
The caecilian is a type of amphibian that has a wormlike body with no limbs. Caecilians are found only in the tropics.

Fire Salamander
Among fire salamanders, the female retains her fertilized eggs within her body until they hatch. The emerging young may either be larvae with gills or fully formed juveniles who possess the body structures of an adult.

Golden Toads
While most toads are camouflaged with brownish or greyish coloration, these golden toads of Costa Rica are an exception. Only the males of the species are bright gold; females are more neutral in color. Here males await females at the breeding pool.

Pictures of Mammals

2008-09-09T20:03:00.000-07:00

Snow Leopard
The snow leopard lives only in coniferous forest scrub areas and the mountain steppe region of the Himalayas and surrounding areas. Generally solitary except during mating season, the snow leopard may be found at altitudes higher than 6000 m (19,000 ft) in search of migratory game such as wild sheep, ibex, and the musk deer.

Sumatran Rhinoceros
The Sumatran rhinoceros (Dicerorhinus sumatrensis) has been hunted so extensively that fewer than 300 animals survive in fragmented populations in Malaysia and Indonesia. Between 1985 and 1995 the number of Sumatran rhinos declined by 50 percent due to poaching.

Sumatran Tiger
The Sumatran tiger, found only on the Indonesian island of Sumatra, is the smallest type of tiger. Females weigh 75 to 110 kg (165 to 240 lb), and males weigh 100 to 140 kg (220 to 310 lb). In recent years the demand for tiger parts across Southeast Asia has threatened the Sumatran tiger, whose skins, bones, and claws are used in folk remedies and as novelty displays.

Tapir
Tapirs, found in dense forests and swampy areas of Central and South America and Asia, are moderately large mammals, growing to a height of 75 to 120 cm (29 to 47 in) and a weight of 225 to 300 kg (500 to 600 lb). The nocturnal animals feed on leaves, grasses, aquatic vegetation, soft twigs, and fruit, using their short flexible snouts to roll up leaves and other vegetation.

Tarsier
Native to rain forest and shrub areas of Indonesia and the Philippines, the arboreal tarsier feeds primarily at night on insects and lizards. The primate has well-adapted hind legs for leaping, and has extremely long fingers and toes equipped with fleshy disks for traction.

Thirteen-Striped Ground Squirrel
Ground squirrels, like this common species from the midwestern United States, are social animals that live in colonies of burrows connected by a network of tunnels. The tunnels help improve the quality of the land by bringing up soil from lower levels but can be quite destructive to agricultural irrigation systems.

Walrus Tusks
The large front tusks, actually elongated canine teeth, appear to be used primarily for helping the walrus haul itself out of the water and onto large ice floes, where it spends long periods of time. Earlier speculation that the tusks were used to probe the bottom sediments in search of food appears to be incorrect. While walruses do search the sea floor for food such as clams, they apparently skim their sensitive whisker pads across the bottom rather than probing with their tusks.

Yorkshire Terrier
Yorkshire terriers are small dogs characterized by long, silky hair. A toy breed, the Yorkshire terrier was originally bred in England and was favored by the aristocracy in the 19th century.

Pictures of Mammals

2008-09-09T20:00:00.000-07:00

Numbat
The numbat, Myrmecobius fasciatus, is an endangered marsupial that lives in southwestern Australia, often in eucalyptus groves. Numbats use their sensitive noses and sticky tongues to find and eat insects, especially termites. During the winter months they warm themselves by basking in the sun. Australians have created captive breeding colonies for numbats in hopes of ensuring their survival.

Pangolin
Four species of terrestrial and arboreal pangolins are found in forest and open savanna habitats of Africa and southern Asia. Entirely covered with large, brown, overlapping scales, the pangolin is well protected against predators. When threatened, the pangolin rolls into a tight ball, causing the sharp, free edges of the scales to rise. Pangolins eat ants and termites, which they lap up with their long, sticky tongues.

Platypus
The duck-billed platypus, Ornithorhynchus anatinus, found only in eastern Australia, lives in streams, rivers, and occasionally lakes with year-round water. It feeds mostly on bottom-dwelling aquatic insect larvae, which it finds by probing the streambed with its pliable, sensitive bill. It grows to a maximum size of 1 to 2.4 kg (2.2 to 5.3 lb). One of only a few venomous mammals, the male platypus has a poison gland in the hind leg that opens through a bony spur on the ankle. The spur is used to defend against predators and possibly to defend its territory against other males. The females lack the venom gland and bony spur.

Polar Bear
Polar bears congregate on the snow-covered shores of Hudson Bay in northeastern Manitoba. All of Manitoba’s rivers and streams drain into the Bay, where the fishing is good for polar bears.

Pronghorn
The pronghorn is one of the fastest mammals on earth, reaching a maximum speed of 86 km/hr (55 mph) and a sustained speed of 70 km/hr (45 mph). Native to the open grasslands and brushlands of the western United States, Canada, and Mexico, the pronghorn feeds on crops and a variety of wild plants. The pronghorn’s eyes are set far out on the skull, allowing for a 360-degree field of view.

Red Wolf
The red wolf, Canis rufus, is smaller than its close relative, the gray wolf. Virtually extinct in the wild, the United States Fish and Wildlife Service is breeding red wolves in captivity. They have had mixed success when the captive-bred red wolves were released into two wilderness sites within their native habitat in the southeastern United States. Some wolves were able to thrive while others died.

Reindeer
The reindeer inhabits the far northern reaches of Europe and Asia, as well as North America, where the animal is called a caribou. Although the population of reindeer has declined, some nomadic tribes in North Asia and Europe and northernmost North America still follow the herds, using the flesh of the animals as food and their antlers as tools and utensils. Massive assymetrical antlers grow on both male and female reindeer; the female reindeer is the only type of female deer to have antlers.

Ring-Tailed Lemurs
The ring-tailed lemur, Lemur catta, is found only on the island of Madagascar and the nearby islands of Comoros. Adults of this species grow to 38 to 43 cm (15 to 17 in) in length and can reach weights of nearly 4 kg (9 lb). Their habitat ranges from tropical deciduous forest to semi-desert, and they are comfortable both on the ground and climbing trees.

Short-Beaked Echidna
Echidnas are monotremes, or egg-laying mammals. The female deposits a single egg in her pouch while lying on her back. The egg hatches only about ten days later, but a young echidna stays in its mother’s pouch, feeding from milk “patches,” until its spines begin to develop. An echidna’s spines are its protection. If threatened, the animal curls up in a ball, offering a mouthful of sharp spikes to its attacker. On soft soil, it will use its long foreclaws to bury itself and escape heat and disturbances. The short-beaked echidna is Tachyglossus aculeatus.

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Pictures of Mammals

2008-09-09T19:56:00.000-07:00

Dall Sheep
Dall sheep, sometimes called thinhorn sheep, inhabit cliff regions in Alpine and Arctic tundra areas of Alaska and northern British Columbia. Related to the musk ox and the moutain goat, these sheep can have either black, gray, or white coats, depending on the subspecies.

Douroucouli
The douroucouli is the only species of monkey that is nocturnal. With its large eyes, it is well adapted to see at night, but it can not perceive colors.

Dugong
This male dugong is among only a few thousand of the large marine mammals believed to remain in the Indian and western Pacific oceans. Dugongs, commonly called sea cows, have long been hunted for their meat, blubber, oil, and hide. The harmless animal uses its rounded forelimbs for locomotion and its muscular lips to tear water plants for food.

Grévy’s Zebra
The Grévy’s zebra (Equus grevyi) is the largest zebra, weighing up to 450 kg (990 lb). The vertical stripes on its body are narrow and close together, covering most of the body except the belly. Grévy’s zebra frequents the plains and brush country of Ethiopia, Somalia, and Kenya.

Hippopotamus
The hippopotamus divides its time between water and land. During the day, its unusually thin outer layer of skin wicks moisture away too quickly for the animal to remain out of water for very long. Instead of sweat glands, the skin has glands that secrete a thick, reddish fluid impenetrable by the sun’s burning rays; for this reason, hippos have been said to “sweat blood.” Hippopotamuses spend the night on land, foraging for the roughly 40 kg (88 lb) of food they consume a day.

Holstein Cow
Dairy farmers raise Holstein cows to produce milk. One Holstein cow can produce around 9,500 kg (21,000 lb) of milk in one year.

Komondor
A komondor is a breed of working dog distinguished by a coat of long, corded white hair that feels like felt.

Minke Whale
The small, lively minke whale is distinguished by a dark-and-light harlequin coloration, including white stripes across the flippers and upper back. When playing, a minke whale may breach, or leap out of the water, at a 45-degree angle, and then arch its back for a smooth reentry, or stretch out horizontally for a loud belly flop. These inquisitive whales sometimes appear alongside a ship, often keeping pace with the vessel for speeds up to 30 knots.

Netherland Dwarf Rabbit
The Netherland Dwarf rabbit is one of the most popular breeds of pet rabbit.

Nine-Banded Armadillo
The nine-banded or common long-nosed armadillo is the most widespread and adaptable of all species of armadillos. It ranges from the southern United States southward into Argentina and Uruguay and feeds on fungi, fruits, tubers, termites, ants, small vertebrates, and carrion.

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Pictures of Mammals

2008-09-09T19:52:00.000-07:00

Arctic Fox
The arctic fox, Alopes lagopus, wears two coats. Its warm-weather coat is gray-brown. During the winter, however, its fur is thick, white camouflage against a landscape of snow and ice, protection both from predators and from the harsh temperatures of tundra latitudes. The fox’s small snout and ears also conserve heat, as do its fur-covered feet, reminiscent of a rabbit’s. Temperatures drop to -70° C (-94° F) before the arctic fox begins to shiver. A small number have blue coloration in colder months, alternating to a rich brown in the summer.

Asian Water Buffalo
Related to the African water buffalo, yak, American bison, European bison, and four-horned antelope, the Asian water buffalo, Bubalus bubalis, has been domesticated and is now found throughout India, Asia, South America, Europe, and southern Africa.

Australian Shepherd
Brought to the United States by sheepherders in the late 19th century, the Australian shepherd possesses strong herding instincts. The Australian shepherd’s natural ability to steer cattle and sheep makes it popular as both a working dog and a pet on many American farms and ranches.

Aye-Aye
The aye-aye belongs to a group of arboreal mammals known as lemurs. This solitary, nocturnal mammal has very large incisors, toes, and fingers. The aye-aye, which is found only in northwestern and eastern Madagascar, feeds primarily on insect larvae and fruits.

Barren Ground Caribou
Unlike other members of the deer family, both male and female caribou have antlers. Antlers are shed and regenerated annually, their growth controlled by sex hormones. In the spring, male antlers have a velvet appearance due to the thin coat of fine hairs that supplies them with nourishing blood flow. Within a few months, antler growth is complete and blood circulation in the velvet ceases. The animal rubs its antlers against a tree to scrape away the dead skin.

Blue Whale
The blue whale, the largest animal ever to exist, may grow over 24 m (80 ft) in length. The loud moans of blue whales may carry through deep waters to distances more than 160 km (100 mi) away, allowing them to communicate across vast areas of water. Hunted nearly to extinction in the first half of the 20th century, blue whales are now protected, although they remain endangered.

Bonobo
The bonobo, or pygmy chimpanzee, and its close cousin, the common chimpanzee, are the closest animal relatives to humans. Bonobos have a particularly peaceful way of life, where affection instead of force is used to establish rank.

Borzoi
The Borzoi, or Russian wolfhound, was bred in Russia in the early 17th century to hunt wolves and rabbits. A swift runner, the dog is characterized by a long, silky coat; a low-hanging tail; and long body.

California Sea Lion
Raising his muzzle and displaying his powerful chest, a California sea lion, Zalophus californianus, takes an aggressive posture to stake out his breeding territory and warn off intruders. If another male sea lion, or a human, approaches him, he will bark loudly and prepare to fight to defend his chosen mating area along the rocky coast.

Chinese Shar-Pei
Chinese breeders originally cultivated the excess folds of skin on the Shar-Pei to give the breed an advantage in dogfights. Considered a working dog since its origin in ancient times, the Chinese Shar-Pei retains an independent demeanor.

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Placentals

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The third subclass of mammals, called placentals, includes about 4300 species, making it by far the largest of all three mammal groups. Unlike young marsupials, young placental mammals spend a relatively long time developing inside their mother’s body before birth. Warm and protected within the mother’s womb, the unborn young are nourished by a spongy organ called the placenta, which absorbs nutrients from the mother's blood and transfers them to the developing animal. By the time a young placental mammal is born it is usually fully formed, although it may not yet have fur or functioning eyes or teeth.

Biologists classify placental mammals into about 19 groups called orders (the exact number varies in different classification systems). The largest group, with about 1500 species, contains the rodents, such as rats, mice, squirrels, and porcupines. Animals with sharp, chisel-like front teeth that grow throughout life, rodents use these teeth to gnaw into their food, and also to cut through any obstacles in their path. Another major group of mammals, with about 1000 species, contains the bats. Insect-eating bats are generally small animals, but some fruit-eating species have a wingspan of over 1.5 m (5 ft).

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Marsupial

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Marsupial, common name for a group of mammals typically distinguished by a pouch in the female, called a marsupium, where offspring are carried. The kangaroo, koala, wombat, and opossum are well-known marsupials, as are other less-familiar animals, such as the numbat, bandicoot, ringtail possum, and thylacine. These unusual creatures range in size from the tiny, mouselike ningaui, which measures about 5 cm (about 2 in) long and weighs a mere 2.8 g (0.1 oz), to the gray and red kangaroos, which can reach lengths of 2.5 m (8 ft), stand up to 1.8 m (6 ft) tall, and weigh 90 kg (200 lb).

Scientific classification: Marsupials make up the scientific order Marsupialia. The Virginia opossum is classified as Didelphis virginiana and the whiptail wallaby as Macropus parryi.

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Echidna

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Echidna, also spiny anteater, common name for a type of egg-laying mammal (see Monotreme). The short-nosed echidna found in Australia is about 35 to 53 cm (about 14 to 21 in) long, exclusive of a short tail, and has a broad body mounted upon short, strong legs. The legs have powerful claws, adapting the animal for rapid digging into hard ground. The back is covered with stiff spines mixed with long, coarse hairs. The head is small, and the nose is prolonged into a slender snout. The toothless mouth has an extensile, glutinous tongue suitable for catching ants, termites, and other small insects. Mating occurs once a year. The female lays one egg, or rarely two eggs, after a gestation period of 9 to 27 days. The female then places the egg in a pouchlike area of abdominal skin, where it hatches after about 10 to 11 days. The offspring is carried in the pouch until it is about 55 days old, when it becomes able to walk. A somewhat larger subspecies of the short-nosed echidna is native to Tasmania. The New Guinean echidna has a long, curved snout and grows as long as 75 cm (30 in). In locations where ants and termites are abundant, the smaller echidnas make useful pets; they are long-lived and, despite their bristly coat, are gentle in disposition. Human beings, who sometimes eat them, are the only natural enemies of echidnas.

Scientific classification: Echidnas belong to the order Monotremata. The short-nosed echidna is classified as Tachyglossus aculeatus, the Tasmanian echidna as Tachyglossus aculeatus setosus, and the New Guinean echidna as Zaglossus bruijni.

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Platypus

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Platypus (Greek platys, “broad”; pous, “foot”), also duckbill, semiaquatic, egg-laying mammal native to Tasmania and southern and eastern Australia. The animal has a bill that resembles a duck bill but is actually an elongated snout covered with soft, moist, leathery skin and sensitive nerve endings. The body of the platypus is 30 to 45 cm (12 to 18 in) long; the flattened tail measures 10 to 15 cm (4 to 6 in) in length. The feet are webbed. The body and tail are covered with a thick, soft, woolly layer of fur, from which long, flat hairs protrude. The most conspicuous feature of the small head is the bill, which is about 6 cm (about 2.5 in) long and 5 cm (2 in) wide and which the animal uses for detecting prey and stirring up mud at the bottom of rivers in order to uncover the insects, worms, and shellfish on which it feeds. The head is joined directly to the body without an apparent neck. The platypus's eyes are small, and it has no external ears, but it has keen senses of sight and hearing. Young platypuses have rudimentary teeth; in adults the teeth are replaced by a few horny plates. Adult males have a hollow, horny spur on the inner side of the hind leg, from which a toxic fluid is ejected and which may be used as a weapon of defense. The call of the platypus is a low growl.

Duckbills are shy animals and are seldom observed, even in localities where they abound. They are active only during the early morning and late evening, and are excellent swimmers and divers. They live in long, winding burrows, which are usually dug by the females in the banks of rivers or streams. The burrows are blocked with earth in several places as fortification against intruders and flooding. At the end of the burrow, which may be from about 9 to 18 m (about 30 to 59 ft) in length, the female constructs a bed of weeds, leaves, and grass, which it uses as a nest for the eggs and young, and for a retreat. The male is excluded from the nesting burrow. The female lays usually two but sometimes as many as four eggs in a clutch. The young animals have no fur when they hatch. The female uses its tail to clasp the young to its abdomen, enabling them to nurse. Platypuses are unfortunately sometimes captured as biological curiosities, but the hunting of platypuses is forbidden by law.

Scientific classification: The platypus makes up the family Ornithorhynchidae, in the order Monotremata. It is classified as Ornithorhynchus anatinus.

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Monotreme

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Monotreme is a common name applied to a group of egg-laying mammals, including the platypus, or duckbill, and the echidnas, or spiny anteaters. Monotremes are native to Australia, Tasmania, and New Guinea. They possess true teeth only during the early stages of embryonic development. After monotreme eggs are hatched, the young are helpless, and, in the case of the echidna, are carried in shallow abdominal pouches. Young monotremes do not have mouth parts suitable for suckling; the liquid produced by the nippleless mammary organ is licked from the belly hair of the mother. The adult male platypus has a fighting spur on each ankle, which secretes a poisonous substance.

Scientific classification: Monotremes belong to the subclass Monotremata. The platypus makes up the family Ornithorynchidae. It is classified as Ornithor hynchus. Echidnas are classified in the genera Tachyglossus and Zaglossus of the family Tachyglossidae

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Types of Mammals

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In biological classification, mammals form one of the six major classes of vertebrate animals. Mammals themselves are divided into three different groups, or subclasses, based on distinctive underlying features: Monotreme, Marsupial, and placentals.

Most large predatory land mammals belong to a group called the carnivores, which contains about 240 species. Some of these animals, such as lions and wolves, rarely eat anything apart from meat, but others, especially bears, have a more mixed diet. Mixed diets are also common in a different group of mammals—the primates. Primates include animals such as lemurs, monkeys, apes, and humans, and most of the 230 species live in trees.

The world's large plant-eating mammals are divided into two major groups. One group, called the artiodactyls, contains animals such as pigs, deer, cattle, and antelope, which have hoofed feet with an even number of toes. The other, a much smaller group called the perissodactylas, includes horses, tapirs, and rhinoceroses, which have an odd number of toes.

Some mammals have adapted to life in the water. The seals, including sea lions and walruses, can sleep and feed in the open ocean but must return to land in order to reproduce. Manatees and dugongs are large, plant-eating mammals that spend their entire lives in the water. The whales, including the huge baleen whales and the dolphins, are well adapted as fast, open-ocean predators. Still, like all other mammals, aquatic mammals would drown if they could not reach the surface to breathe.

Mammal

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Mammal, animal that raises its young on milk. Most mammals are covered with hair or fur, and most have specialized teeth that help them to cut or chew their food. Compared to other vertebrates (animals with backbones), mammals have highly developed nervous systems, and they show an intelligence and resourcefulness that few other animals can match. Mammals include some of the most familiar members of the animal kingdom, such as cats, dogs, elephants, and whales, and also human beings—a species that now dominates life on earth.

With the exception of three highly unusual mammals called monotremes, all mammals give birth to live young. Some young mammals are completely helpless when they are born, while others are relatively well developed. Despite these differences, all young mammals initially rely on their mothers for food, and stay with them until they are ready to fend for themselves. This close link between mother and offspring produces strong family ties, and allows young mammals to learn by copying their parents' behavior.

Mammals evolved from a group of reptiles called therapsids. The earliest true mammals, appearing over 200 million years ago, were only 5 cm (2 in) long and probably spent at least some of their lives in trees. These tiny mammals resembled shrews with four roughly equal short legs and sharp claws. Since that time mammals have evolved an extraordinary variety of body shapes and sizes.

Mammals have adapted to some of the most extreme habitats on earth. They are warm-blooded, or endothermic, meaning that they maintain their body temperature within a narrow range despite changes in the environment. Polar bears survive on Arctic ice, while Arctic foxes can sleep on open snow in temperatures as low as –68° C (-90° F). Camels and kangaroo rats live in deserts, and can tolerate blazing temperatures that would kill many animals from cooler habitats.

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Ctenophora

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Comb Jellies, a phylum of about 100 widely distributed marine animals resembling jellyfish. The comb jellies have eight rows of comblike plates arranged longitudinally around the body. The plates are moved back and forth in a rippling motion and serve to propel the animal through the water. Most species have two long tentacles at either side of the transparent body, which are used to capture prey. In general the bodies of comb jellies are oval, with a throat opening into the body cavity. They have no separate digestive system, the particles of food being ingested by the individual cells within the body. A sense organ at the opposite end of the body from the mouth is composed of a mass of tiny bony particles, supported away from the body on four legs. Impulses from this organ pass through the legs and into the body of the animal along grooves in the body that contain a large number of hairlike cilia. These grooves, although not true nerves, perform a similar function. Most of the ctenophores are only 7.5 to 10 cm (3 to 4 in) long. One species commonly called Venus's-girdle has a ribbonlike body about 1.5 m (about 5 ft) long, with a mouth on one edge of the center of the ribbon.

Scientific classification: Comb jellies make up the phylum Ctenophora. The Venus's-girdle is classified as Cestum veneris.

Anthozoa

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In the Anthozoa class there is no medusa stage. An anthozoan polyp reproduces sexually, although the polyps of some species also reproduce asexually. Asexual reproduction results in a colony if the daughter polyps remain attached to one another. There are about 6,500 species of anthozoans, including corals, sea anemones, sea pens, and sea fans (see Gorgonian).

Orange tube-coral

Orange tube-coral does not grow in areas of dense coral development. Instead it thrives on the sides of boulders, underhangings, and drop-offs. This type of coral can also be seen in tide pools.

Cubozoa

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The medusa phase dominates in animals in the Cubozoan class. Cubozoan medusae are commonly called box jellies because they have a cube shape with a single tentacle or group of tentacles hanging from each corner at the mouth end of the animal. The Cubozoan polyp is small and inconspicuous and an entire polyp transforms into a medusa in a type of asexual reproduction. Cubozoa consists of about 20 species of sea wasps and their relatives. The nematocyst sting of some cubozoans, including the Australian sea wasp Chironex fleckeri, contains poison that can be fatal to humans.

Jellyfish

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Jellyfish, common name for any of the invertebrate animals making up two classes of the cnidarian phylum. About 2700 hydrozoan and 200 scyphozoan species are known. The term jellyfish applies more specifically to the free-swimming, gelatinous organism called the medusa, the form usually taken during the sexual stage of these animals, this generation alternating with a bottom-dwelling polyp stage in which reproduction is asexual. In one class the medusae tend to be small and the polyps well developed, whereas in the other class the medusae predominate. Both classes are marine, except for a few hydrozoans, such as Hydra, that live in fresh water.

Jellyfish have little nutritional value. Their stings can be painful, and a few tropical forms can be deadly to humans.

As in other cnidarians, the jellyfish has only two major developmental layers (ectoderm and endoderm), no head, a gut but no anus, and a nervous system without a brain. The body exhibits radial symmetry, or symmetry about an axis. Prey are usually taken with tentacles bearing nematocysts, or stinging cells. The polyps commonly live on the sea bottom and produce other polyps by asexual reproduction. Hydrozoan polyps generally form colonies, with different kinds of polyps specialized for such functions as reproduction and feeding. The polyps usually bud off medusae.

Ordinarily, the medusae produce eggs and sperm that unite and give rise to a new generation of polyps. The medusae are bell shaped and swim by contraction of muscles around the rim. Their behavior is simple. Most swim slowly and are transported by currents. Transparency results partly from the fact that a jellyfish body contains less than 1 percent organic matter—the rest is water. Large jellyfish are up to 2 m (6.6 ft) wide.

Scientific classification: Jellyfish make up the classes Hydrozoa, with well-developed polyps, and Scyphozoa, in which medusae predominate, of the phylum Cnidaria.

Scyphozoa

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The medusa phase dominates in most of the 200 species of scyphozoans, the cnidarians most frequently referred to as jellyfish. Scyphozoan medusae are larger and have a more complicated structure than the short-lived medusae of the hydrozoans. Scyphozoan medusae live several months or more, reproducing sexually to form small, inconspicuous polyps. Polyps reproduce asexually to form a medusa—saucer-like structures bud off the polyp and swim away as new medusae.

Portuguese Man-of-War

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Portuguese Man-of-War
The Portuguese man-of-war is actually a colony of specialized polyps that all contribute to the well being of the colony by performing specific tasks, such as feeding or providing buoyancy control. The man-of-war has a relatively large, gas-filled bladder that provides flotation for the entire colony. A large collection of feeding polyps suspended from the underside of the float, each with a single, long tentacle, captures and digests food, which is then shared with the entire colony by means of interconnecting digestive cavities. Although the Portuguese man-of-war resembles a jellyfish, it belongs to Class Hydrozoa in the phylum Cnidaria, while true jellyfish belong to Class Scyphozoa in the same phylum.

Hydrozoa

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Hydrozoa, class of invertebrates belonging to the cnidarian phylum. The hydrozoans make up six orders. Most species of hydrozoans show alternation of generations. One generation consists of individuals called polyps and is almost always colonial; the colony is known as a hydroid because of the resemblance of its individual polyps to the noncolonial hydra, the simplest of all hydrozoans. The other generation, members of which are known as medusae, consists of free-swimming, sexual individuals that produce either eggs or sperm; the familiar jellyfish is a typical medusa. Each fertilized egg develops into a ciliated larva (planula), from which the hydroid develops and then gives rise to medusae by budding.

Hydrozoans differ in their conformity to the typical alternation of generations. The order to which the hydra belongs has small medusae and sometimes no free-swimming forms at all. The siphonophoran order, containing the Portuguese man-of-war, has a short-lived medusa stage, the larvae of which develop into medusalike organisms from which the colony arises. The individual members of a siphonophoran colony are extremely specialized; the polyps specializing in defense produce a venom strong enough to kill a human being. Another order has a short-lived polyp stage; in some species no polyp stage has yet been observed. Its members spend most of their lives as free-swimming medusae. A fourth order combines traits of polyps and medusae, somewhat resembling free-swimming, ciliated hydras. The two primarily tropical orders contain a number of interesting forms that secrete a large, hard, calcareous exoskeleton and often form corals.

Scientific classification: The class Hydrozoa belongs to the phylum Cnidaria. Hydra belong to the order Hydroida, siphonophores to the order Siphonophora. Species with a short-lived or nonexistent polyp stage belong to the order Trachylina. Species resembling free-swimming polyps belong to the order Actinulida. The two primarily tropical orders are Stylasterina and Milleporina; the latter is sometimes considered a suborder.

Pictures of Invertebrates

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Purple and Yellow Tube Sponge
The purple and yellow tube sponge displays one of the many different body forms typical of sponges. Sponges, considered to be the most primitive of the multicellular animals, are represented in the fossil record back to the Cambrian Period, at least 600 million years ago. The interior body cavities of sponges provide shelter for a variety of small crabs, sea stars, and other marine invertebrates.

Scorpion
This species of scorpion is one of approximately 40 species of scorpion native to the southwestern United States. A jointed, external exoskeleton provides the scorpion with a protective outer shell. Defense and prey capture involves grasping of the prey or potential predator with the large powerful claws while the jointed tail delivers a disabling sting. Although the sting of most scorpions is not fatal to humans, the sting of this particular species has proven to be fatal to younger children.

Sheep Tick
Ticks are members of the class Arachnida, which includes spiders, scorpions, daddy longlegs, and mites. All ticks are carnivorous, feeding on the blood of various species of birds, reptiles, and mammals, including human beings. Ticks use their mouthparts to anchor themselves to the skin, where they cut a small hole and suck the blood. A number of tick species transmit diseases infecting livestock, pets, and humans.

Silverfish
The silverfish, like other insects of its order, displays vestigial legs in addition to the usual six. Among the most primitive of all animals, the silverfish belongs to the bristletails order of insects. A common household pest also known as “sugar mites,” silverfish feed on starchy materials such as foods in kitchen pantries and the glue in book bindings and wallpaper.

Snail
Some groups of snails have shells that coil to the left (left-handed), while others have shells coiling to the right (right-handed). In some groups both right- and left-handed members are present. The shell affords protection from predators and the rigors of the environment. When threatened, the snail pulls its entire body inside. A small, circular structure called the operculum closes securely behind the snail to form a tight seal that keeps out predators and keeps in moisture.

South African Tsetse Fly
The South African tsetse fly, common to central Africa, is responsible for transmitting the parasitic protozoan that causes sleeping sickness, a disease that can be fatal to humans and domestic cattle.

Sow Bug
The sow bug is actually a type of crustacean. Sow bugs are commonly found in rotting wood, wood piles, or under the loose bark of old stumps or fallen trees. When threatened by predators, the sow bug curls up into a tight, little ball, protected by its hard outer shell.

Starfish
Although many starfish have 5 arms, or rays, some species may have as many as 44 arms. All starfish can grow back arms lost through predation and physical injury. Starfish have a flattened body with the mouth located on the oral, or lower body surface. Many starfish can evert their stomach through their mouth to feed on food items too large to ingest.

Tapeworm
Tapeworms are parasitic worms that infest the intestinal lining and other organs of vertebrates. Tapeworms, having no mouth or digestive tract, are able to absorb partially digested material through their body surface.

Velvetworm
The velvetworm is an unusual animal because it shares some characteristics with arthropods but has other features that resemble segmented worms, or annelids.

Zebra Mussel
Accidentally introduced from Europe in the mid-1980s, zebra mussels have spread throughout many North American lakes and rivers. These hardy freshwater mussels grow and reproduce quickly. They attach to almost any submerged surface, frequently coating or clogging boat hulls, fishing equipment, and water intake pipes.

Pictures of Birds

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Robin
Both European and American robins typically live close to human dwellings. The American robin eats mainly fruit, although it occasionally eats insects.

Snowy Owl
The snowy owl ranges across northern Eurasia and North America. During the winter months, the snowy owl’s white plumage camouflages it, allowing it to swoop down undetected on small mammals and fish.

Surf Scoter
The surf scoter, Melanitta perspicillata, is a migratory duck that spends its summers in Arctic tundra and muskeg regions of Canada and Alaska and its winters from southern California and the Gulf of California eastward to Florida. Surf scoters feed on insects, larvae, and pondweed.

Tropical Parrots
Florida’s warm, humid climate allows it to sustain exotic tropical wildlife like these parrots, originally from South America.

Vegetarian Finch
On visiting the Galápagos Islands in 1835, British naturalist Charles Darwin noted the diversity of life, with each island supporting its own form of tortoise, mockingbird, and finch, such as the vegetarian finch shown here. Darwin suspected that geographic isolation had caused a single species to gradually evolve into a number of diverse species. This theory of evolution by natural selection, as explained in his 1859 work On the Origin of Species, revolutionized understanding of the natural world.

Western Grebe
The graceful western grebe, Aechmophorus occidentalis, is well suited for life in water but cannot walk on dry land. The bird uses a variety of elaborate dances during courtship. The mating pair, shown here, race side-by-side across the water with their heads erect and their bodies pushed up out of the water.

White-Tailed Kite
The white-tailed kite, Elanus leucurus, lives in open country in the western United States south through Mexico into parts of Chile and Argentina. Like many members of the hawk family it hunts by soaring over open areas looking for field mice and other small mammals. Populations of this graceful long-winged kite are making a comeback after being hunted almost to extinction early in the 20th century.

Wood Duck
The wood duck, Aix sponsa, lives in a variety of freshwater habitats in Canada, the United States, and Mexico. It often swims in shallow water, foraging for the seeds of aquatic plants. Like other ducks, the wood duck has webbed toes that function as paddles.

Pictures of Birds

2008-09-09T07:03:00.000-07:00

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Great Gray Owl
The great gray owl, Manitoba’s provincial bird, is one of many kinds of wildlife that live in the undeveloped forests of the province. Because its home is in the far north where it stays light much of the time, this owl must often hunt in daylight. Owls, which are generally nocturnal, prefer to hunt at night.

Great Kiskadee
Named for its loud kis-ka-dee call, the great kiskadee, Pitangus sulphuratus, inhabits open country from the southern United States to Argentina. Like other members of the flycatcher family, it feeds mainly on large insects that it catches in flight.

Green Heron
The green heron, Butorides virescens, is a small, solitary bird that lives among dense vegetation along the banks of ponds and marshes. It often sits in tall grass leaning motionless over the water watching for small fish to swim past. It strikes quickly at prey, seldom missing with its pointed bill.

Hawfinch
Native to Europe, Africa, and Asia, the shy hawfinch, Coccothraustes coccothraustes, is the largest member of the finch family. It is distinguished by its large, powerful bill, which it uses to crack open a variety of hard seeds. The bill changes from gray in winter to blue-black in spring.

White Egret
A great white egret flies with twigs for its nest. Egrets were nearly hunted into extinction for their feathers, which were used to decorate hats. Now they are protected by legislation.

Ivory-billed Woodpecker
John James Audubon’s Ivory-billed Woodpecker is from The Birds of North America, published between 1827 and 1838. Audubon was a perfectionist and went out into the field to collect specimens to work from in his studio. His work has the clarity and attention to detail that characterize high-quality scientific illustration, as well as the feeling for composition and line quality that characterize fine art.

Penguin
Penguins always return to their ancestral nesting sites to lay their eggs and rear their young. The emperor penguin, the largest of the penguins, lays its single egg during the coldest time of the Antarctic year, when temperatures drop as low as -62 degrees C (-80 degrees F). The egg is incubated on top of the parent’s feet, protected by abdominal folds of skin. Young chicks remain under these abdominal folds until they are able to regulate their own body temperature.

Purple Gallinule
The purple gallinule, Porphyrula martinica, ranges from South Carolina to South America. A powerful swimmer, the cootlike gallinule is less successful in flight. The bird spends most of its time hiding among the grasses of its marsh habitat. It forages on the muddy shores for small invertebrate animals and vegetation. Unlike other members of the rail family, the gallinule bill is too short to probe beneath the surface.

Red-Tailed Hawk
The red-tailed hawk, Buteo jamaicensis, is the most abundant hawk in North America. Although its plumage varies, all adults have a characteristic reddish-brown tail. It hunts by gliding over open countryside searching for rodents, insects, birds, and snakes.

Rhode Island Red
The Rhode Island Red, prolific year-round, is one of several American class breeds valued for the number and quality of its eggs.

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Pictures of Birds

2008-09-09T06:58:00.000-07:00

Common Snipe
The common American snipe is one of 81 species of sandpiper, which comprises the largest family of shorebirds. All sandpipers have relatively long wings and short tails, but differ greatly in the shape of their bills. The snipe can be found in swampy marshes and other wet habitats, where it uses its long, slender bill to probe for aquatic insects, snails, and small crustaceans.

Emu
The emu, Dromiceius novae-hollandiae, is a large, flightless bird native to Australia. Emus roam the western half of the continent in mass movements that may involve as many as 70,000 birds. They depend on the fruits, seeds, and flowers that grow in areas of recent rainfall and must migrate once they have depleted local sources. Frustrated farmers have constructed a 1000 km (600 mi) fence barring the emus from inland agriculture. Only when the males, which hatch and raise the young, are nesting are the giant birds tied to one location.

European Goldfinch
The European goldfinch, Carduelis carduelis, lives in open country where it feeds on the seeds of thistles and other weeds. Native to Europe and parts of Africa and Asia, this colorful songbird has been successfully introduced to Australia and South America. Its cheerful call is a repeated tswitt-witt-witt.

Feral Pigeon
Although pigeons are regarded as pests by many city dwellers, they are fairly unique in the bird world. They drink with their beaks underwater, actually sucking water through the nostrils. They are also the only bird besides the flamingo to produce a milklike crop secretion very similar in consistency and function to that of mammals. The feral pigeon is one of several breeds of rock pigeon, Columba livia. Although the bird pictured here hitched a ride from Liverpool, England, to Caracas, Venezuela, on a merchant ship, other members of its species typically migrate thousands of miles, maintaining speeds of up to 70 km/h (44 mph).

Flamingo
Colorful flamingos are found in lagoons and lakes in parts of the Galápagos Islands. Flamingos feed on microscopic life that they strain from the water and mud with their sievelike bills.

Franklin’s Gull
Not all gulls are seagulls. Also called prairie pigeon or prairie dove, the Franklin’s gull has adapted to life far from the ocean. It lives on the lakes and marshes of the Great Plains where it forages for insects, seeds, and fish. During the breeding season each mating pair builds a large floating nest out of cattails and other plants.

Godwit
Godwits live on the tidelands and prairies of Europe, Asia, and the Americas. These large, long-legged sandpipers may have been named for their ringing god-wit call. Godwits graze in shallow water by probing with their long pointed bills for insects, snails, and marine worms.

Golden Eagle
The golden eagle, found in northern North America, Europe, Asia, and North Africa, is one of thirty species of booted eagles, so named because of their completely feathered legs. The golden eagle has an involved aerial courtship display.

Goldeneye
The bright yellow eyes of this stocky duck contrast with its dark purple or green head. The female, shown here, has brownish-gray and white plumage. Goldeneyes are strong swimmers who can dive to depths of 6 m (20 ft) or more in search of food. They feed primarily on aquatic insects, crayfish, and plants.

Gouldian Finches
Gouldian finches are one of about 153 species of finches found worldwide. The bills of finches are structurally adapted for shelling seeds, their primary food. A seed wedged in a small groove on the side of the palate is crushed when the lower portion of the bill is raised up against it. The tongue then removes and discards the husk, after which the seed is swallowed.

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Pictures of Birds

2008-09-09T06:50:00.000-07:00

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Bald Eagle
Designated as the national bird of the United States in 1782, the bald eagle is the second-largest bird of prey in North America, after the California condor. The bald eagle population has shrunk due to exposure to insecticides such as DDT and other toxins, but is now recovering in some areas.

Barred Plymouth Rock Hen
The barred Plymouth Rock hen is an American class chicken, categorized with other medium-sized, yellow-skinned fowl developed in the United States. Selectively bred from Asian, English, and Mediterranean stock, this species is valued for the quality of its meat.

Black Duck
The black duck, Anas rubripes, is a close relative of the mallard. It lives near bodies of freshwater throughout eastern North America. Black ducks are best adapted for life in wooded areas and have been hurt by the widespread clearing of forests within their range.

Black Turnstone
This plump sandpiper lives along the rocky coastlines of North America’s Pacific coast. The black turnstone, Arenaria melanocephala, feeds mostly on shellfish such as limpets and barnacles, and also on insects and seeds. It has a white belly that contrasts with its black head and back. During the winter its plumage changes from black to dark gray.

Burrowing Owl
The burrowing owl, Speotyto cunicularia, lives in the open grasslands and farmlands of eastern Canada and the United States. This brown and white owl hunts for small mammals, birds, and reptiles for most of the year, but switches to insects during the summer. Burrowing owls typically nest in burrows that have been abandoned by prairie dogs and other animals.

California Condor
The California condor, considered for years to be the most endangered species of bird in the United States, was removed from the wild in 1988 in an attempt to increase its numbers through captive breeding programs directed by the U.S. Fish and Wildlife Service.

Canada Goose
The Canada goose, Branta canadensis, is North America’s most common goose. Naturally migrating as far north as arctic Canada and as far south as central Mexico, it is gradually becoming a year-round resident in grassy suburbs throughout much of Canada and the United States. It grazes on the stems and shoots of grasses and can reach weights of 11 kg (24 lb).

Clapper Rail
The clapper rail, Rallus longirostris, found in salt marshes along the Atlantic Coast, grows to an adult size of 40 cm (16 in). It lays 6 to 15 white or buff-colored, spotted eggs in nests constructed out of grasses and reeds on the ground in meadows.

Common European Crane
The common European crane, a member of one of the oldest orders of birds, has evolved a number of complicated behaviors, called dances, which include the nestling’s excited bobbing on the return of its parents, the social dancing of adolescent birds, and the precopulatory dances of new mating pairs. Cranes will also dance spontaneously within a group or when agitated. The dances help curb aggression and form or strengthen relationships.

Common Rhea
The common rhea is the largest flightless bird in the western hemisphere. Ranging throughout the grasslands of South America south of the Amazon, the gregarious rheas feed on insects when young, but soon switch to an adult diet of vegetation. Rheas have long been hunted for their feathers, eggs, and meat.

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Types of Birds and Examples

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1. Anseriformes -> Waterfowl (ducks, geese, swans)
2. Apodiformes -> Swifts, hummingbirds
3. Caprimulgiformes ->Goatsuckers, nightjars
4. Charadriiformes -> Shorebirds, gulls, alcids, jacanas, skuas, terns, skimmers, oystercatchers, avocets
5. Ciconiiformes -> Herons, storks, ibis, spoonbills, bitterns
6. Coliiformes -> Colies
7. Columbiformes -> Pigeons, doves, sandgrouse
8. Coraciiformes -> Kingfishers, bee-eaters, rollers, hoopoes, hornbills, motmots, todies
9. Cuculiformes -> Cuckoos, anis, roadrunners, hoatzins
10. Falconiformes -> Vultures, hawks, eagles, falcons, osprey, secretary birds
11. Galliformes -> Grouse, pheasants, turkeys, quails, ptarmigans, megapods, guinea fowl, guans
12. Gaviiformes -> Loons
13. Gruiformes -> Cranes, rails, bustards, limpkins, coots, gallinules, buttonquails, sunbitterns, kagus, trumpeters
14. Passeriformes -> Perching birds (over 70 families), including crows, thrushes, sparrows, swallows, wrens, warblers, flycatchers, larks, nuthatches, vireos, shrikes, blackbirds
15. Pelecaniformes -> Pelicans, boobies, cormorants, gannets, darters, frigatebirds
16. Phoenicopteriformes -> Flamingos
17. Piciformes -> Woodpeckers, honey guides, toucans, jacamars, puffbirds, barbets
18. Podicipediformes -> Grebes
19. Procellariiformes -> Albatrosses, shearwaters, petrels
20. Psittaciformes -> Parrots
21. Sphenisciformes -> Penguins
22. Strigiformes -> Owls
23. Struthioniformes -> Ostriches, rheas, kiwis, cassowaries, emus
24. Tinamiformes -> Tinamous
25. Trogoniformes ->Trogons

See pictures of birds

Bird

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Bird, animal with feathers and wings. Birds are the only animals with feathers, although some other animals, such as insects and bats, also have wings. Nearly all birds can fly, and even flightless birds, such as ostriches and penguins, evolved from flying ancestors.

Birds are members of a group of animals called vertebrates, which possess a spinal column or backbone. Other vertebrates are fish, amphibians, reptiles, and mammals. Many characteristics and behaviors of birds are distinct from all other animals, but there are some similarities. Like mammals, birds have four-chambered hearts and are warm-blooded—having a relatively constant body temperature that enables them to live in a wide variety of environments. Like reptiles, birds develop from embryos in eggs outside of the mother’s body

This diagram illustrates some of the important anatomical structures common to birds. Many of these structures are adapted for greater efficiency in flying. The digital and wrist bones of the wing are fused to form ridged support for the flight feathers and the large sternum helps support muscles used in flying. The bones of many adult birds are hollow rather than filled with marrow, making them lighter and enabling them to disperse heat in flight.

All birds are covered with feathers, collectively called plumage, which are specialized structures of the epidermis, or outer layer of skin. The main component of feathers is keratin, a flexible protein that also forms the hair and fingernails of mammals. Feathers provide the strong yet lightweight surface area needed for powered, aerodynamic flight. The wings are highly modified forelimbs with a skeletal structure resembling that of arms. The shape of a bird’s wings influences its style of flight, which may consist of gliding, soaring, or flapping. Wings are powered by flight muscles, which are the largest muscles in birds that fly.

Nearly all birds have a tail, which helps them control the direction in which they fly and also plays a role in landing. The paired flight feathers of the tail, called retrices, extend from the margins of a bird’s tail. Smaller feathers called coverts lie on top of the retrices.

Birds have two legs; the lower part of each leg is called the tarsus. Most birds have four toes on each foot, and in many birds, including all songbirds, the first toe, called a hallux, points backwards. Bird toes are adapted in various species for grasping perches, climbing, swimming, capturing prey, and carrying and manipulating food.

Birds have toothless, lightweight jaws, called beaks or bills. The eyes of birds are large and provide excellent vision. They are protected by three eyelids: an upper lid resembling that of humans, a lower lid that closes when a bird sleeps, and a third lid, called a nictitating membrane, that sweeps across the eye sideways, starting from the side near the beak. This lid is a thin, translucent fold of skin that moistens and cleans the eye and protects it from wind and bright light. The ears of birds are completely internal, with openings placed just behind and below the eyes. The throats of nearly all birds contain a syrinx (plural, syringes), an organ that is comparable to the voice box of mammals. The syrinx has two membranes that produce sound when they vibrate.

Birds have well-developed brains, which provide acute sensory perception, keen balance and coordination, and instinctive behavior, along with a surprising degree of intelligence.

Scientific classification: All birds belong to the class Aves, which is subdivided into 27 orders.

See Types of Birds; Pictures of Birds

Gavial

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Gavial (also spelled gharial), common name for a carnivorous reptile in the crocodile order, noted for its extremely long and narrow snout that sets it apart from other crocodilians. At the end of the snout of mature males is a fleshy lump in which the nostrils are set. Gavials were formerly found in parts of river systems in Pakistan, India, Nepal, Bangladesh, and Myanmar (formerly known as Burma), but today their range is much reduced because of exploitation by humans. Gavials eat fish and are considered too timid to be dangerous to humans. They are generally a pale olive to tan color with dark blotches on the body and tail. The Indian gavial has been known to reach a length of about 6 m (about 21 ft). The Malayan gavial, also known as the false gavial, belongs to a different subfamily and is much smaller, reaching only about 4 m (about 13 ft).

Scientific classification: The gavial belongs to the subfamily Gavialinae, family Crocodylidae, order Crocodilia. The Indian gavial is classified as Gavialis gangeticus. The Malayan, or false, gavial belongs to the subfamily Crocodylinae, family Crocodylidae, and is classified as Tomistoma schlegelii

Caiman

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Caiman or Cayman, common name for three genera of reptiles in the crocodilian order. They closely resemble alligators except for the small bony scales, or osteoderms, embedded in the skin of their bellies. All are found in the American Tropics. The largest—4.5 m (15 ft) or more in length—is the black caiman of the Orinoco and Amazon rivers; it is in danger of extinction, as are many other crocodilians. The smallest caiman, about 1.5 m (about 5 ft), is Cuvier's dwarf or armored caiman, which has heavily ossified, or bony, skin. One of the most abundant and wide-ranging is the spectacled caiman, named for the bony ridge between its eyes, which looks like the nosepiece of a pair of eyeglasses. See Crocodile.

Scientific classification: Caimans belong to the family Alligatoridae in the order Crocodilia. The black caiman is classified as Melanosuchus niger, the armored caiman as Paleosuchus palpebrosus, and the spectacled caiman as Caiman crocodilus crocodilus.

Alligator

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Alligator (Spanish el lagarto,”the lizard”), common name for two carnivorous reptiles in the crocodilian order. Alligators and their close relatives the caimans have broad, flat, and rounded snouts, as opposed to the longer, sharper snouts of other crocodilians; also unlike other crocodilians, their lower teeth cannot be seen when their mouths are closed. Alligators feed on fish, frogs, snakes, turtles, birds, mammals, and carrion. In North America they are also known to attack humans occasionally. Alligators can survive a wider range of temperatures than other crocodilians, and they are found in more temperate regions. Their breeding season is generally restricted to spring.

When alligators search for a mate they bellow often, perhaps to announce their presence to females and to warn other males to stay away. Unwanted intruders are confronted with ritual gaping, lunging, and hissing, but courtship behavior is sedate. After mating, the male seeks his own territory while the female builds a nest of mud and plants nearby, above flood level. The eggs, from 30 to 60 in a clutch, are covered with mud and vegetational debris. The female stands guard as the eggs incubate in the heat from this decaying vegetation and from the sun. When the eggs are ready to hatch, in about 60 days, the young begin to croak softly within the egg. The female may then assist the young in escaping from the nest and may even carry them in her mouth to the water's edge. The female may remain near her young for a year or more. A young alligator in distress will give a series of sharp croaks that may quickly bring the female to investigate.

See Crocodile; Caiman.

Scientific classification: Alligators constitute the genus Alligator, family Crocodylidae. They are sometimes recognized as a separate family, Alligatoridae. The Chinese alligator is classified as Alligator sinensis and the American alligator as Alligator mississipiensis.

Tuatara

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Tuatara, common name for two species of lizardlike reptiles, the only surviving species of an order that flourished about 200 million years ago during the Jurassic period. Tuataras are found only on about 30 islands off the coast of New Zealand. Stocky and big-headed with a strong tail and a spiny crest down the back, they differ from lizards in having a complete lower temporal arch on the skull behind the eye. Tuataras may grow to a length of about 60 cm (about 24 in), usually taking 20 years to reach maturity. They are solitary, burrowing reptiles, feeding mostly at night on insects, lizards, snails, and bird chicks and eggs.

Scientific classification: Tuataras make up the genus Sphenodon of the family Sphenodontidae, order Rhynchocephalia. They are classified as Sphenodon punctatus and Sphenodon guntheri.

Crocodile

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Crocodile (reptile), common name for any of a number of reptiles in a family of the crocodilian order. The term crocodilian refers to all members of the order, which includes alligators, caimans, and gavials as well as crocodiles.

Crocodilians are well-adapted as predators, with few natural enemies. Bony plates, called osteoderms, form a kind of armor in their thick skin. Their teeth, about 30 to 40 in each jaw, are set into sockets in the jawbones and interlock when the mouth is closed. In crocodiles, the fourth tooth on each side of the lower jaw protrudes when the mouth is closed; in alligators, these teeth are not visible. The jaws of crocodilians are powerful enough in closing to crush the bones of small animals, but so weak in opening that they can be held together by hand. As the crocodilian floats almost completely submerged, its protruding nostrils and eyes and a portion of its back are the only parts visible as it stalks its prey. Crocodilians are the most vocal reptiles, producing sounds from quiet hisses to fearsome roars and bellows, usually during the mating season. On land, crocodilians move quickly in a belly crawl but can also gallop and walk mammal-like on all four legs.

Crocodiles are physiologically the most advanced reptiles; their internal anatomy resembles that of birds. They have a four-chambered heart and well-developed senses. Cold-blooded like all reptiles—their body temperature depends on the environment—crocodilians bury themselves in mud to estivate or hibernate. In warm regions they are dormant during droughts; in colder regions, during winter.

Scientific classification: Crocodiles belong to the genera Crocodylus,Osteolamus, and Tomistoma of the family Crocodylidae, order Crocodylia. The Indo-Pacific crocodile is classified as Crocodylus porosus, the swamp crocodile as Crocodylus palustris, the Nile crocodile as Crocodylus niloticus, the Cuban crocodile as Crocodylus rhombifer, the Morelet's crocodile as Crocodylus moreletii, the Orinoco crocodile as Crocodylus intermedius, and the American crocodile as Crocodylus acutus.

Snake

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Snake (reptile), legless animal with a long, flexible body covered with overlapping scales. Snakes are reptiles, a diverse group of animals that also includes lizards, turtles, and crocodiles. Snakes are thought to have evolved from lizards and share many characteristics with this group—particularly the so-called legless lizards, which have tiny, almost imperceptible legs. But unlike most lizards, snakes have thin, forked tongues, and they lack external ears. And while most lizards have movable eyelids that periodically close to protect and lubricate the eyes, a snake’s eyes are always open, protected by immobile, transparent scales.

Like all reptiles, snakes are cold-blooded, or more correctly, ectothermic—that is, they cannot produce their own body heat. Instead, they rely on the sun to heat their bodies and then regulate their temperature with behavior. Because they do not rely on energy from food to generate body heat, snakes can survive on an extremely meager diet. Some wait for months between successive meals, and a few survive by eating a single, large meal just once or twice a year. When they do eat, snakes swallow their prey whole rather than biting off small pieces. Many snakes have specialized jaws that enable them to swallow animals that are far larger than their own heads. Although uncommon, some snakes, such as the African rock python, have been observed eating animals as large as an antelope or a small cow.

Although all snakes have a long, cylindrical body, many species boast unique modifications suited to particular habitats and lifestyles. Burrowing snakes, for example, have muscular, stout bodies and solidly built heads that they use to push through soil. Sea snakes have flattened, paddlelike tails for swimming, and the long, thin shape of many arboreal, or tree-dwelling, snakes provides agility when navigating between branches. Some snakes, including pythons, retain characteristics that reflect their evolution from lizards or from lizardlike ancestors. These snakes have traces of hind limbs called spurs, which are usually more prominent in males than in females.

The smallest snakes are the blind snakes. One member of this group, the Texas slender blind snake, reaches just 13 cm (slightly more than 5 in) in length when full grown and weighs less than 2 g (less than 0.1 oz). The largest snakes are the anaconda and the reticulated python, both of which grow as long as 10 m (about 33 ft) and can weigh up to 250 kg (about 550 lb). Among most species of snakes, females are larger than males.

Scientific classification: Snakes make up the suborder Serpentes in the lizard and snake order, Squamata, in the class Reptilia.

Worm Lizard

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Worm Lizard, common name for wormlike reptiles that belong to the same order as lizards and snakes. This usually limbless reptile lacks external ears and has reduced eyes, a compact skull, and skin with rings of scales. Worm lizards are found in tropical areas throughout the world, usually in underground burrows, where they feed on insects and worms. One species occurs in Florida.

Scientific classification: Worm lizards make up the suborder Amphisbaenia of the order Squamata.

Lizard

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Lizard, common name for certain reptiles in the order that also contains snakes, amphisbaenians (Worm Lizard), and the extinct mosasaurs. Lizards constitute the largest living group of reptiles, with more than 4,300 species in a wide variety of shapes and sizes.

Although lizards may resemble salamanders and other amphibians, they differ in that lizards have dry scaly skin, and most have clawed feet and external ear openings. Most lizards are small, with four legs and a long tail that in many species is fragile and easily broken but will regenerate; the tail of such arboreal species as the chameleon is adapted for grasping branches. The legs of some lizards are greatly shortened, or vestigial, making animals such as the glass lizard or slowworm snakelike in appearance; they are distinguished from true snakes by their movable eyelids and by differences in the structure of the skull bones, especially those of the lower jaw. The bones of the two halves of a lizard’s lower jaw are firmly united; those of a snake are separable.

Lizards move in a variety of ways, depending on body structure and habitat. The collared lizard and the basilisk run quickly on well-developed hind legs. Geckos have scaled disks on each toe that allow them to cling to smooth surfaces. Some lizards are good swimmers, and a number are adapted for climbing trees.

The diets of lizards vary greatly, depending on species. While most are insectivorous, some, such as the green iguana, are generally vegetarians. The Gila monster, which lives in desert areas, eats reptile and bird eggs as well as small rodents; it also has a fat reserve stored in its tail. Depending on their size, monitors prey on insects, birds and reptiles and their eggs, small mammals, and carrion. One species, the Komodo dragon, is large enough to be a threat to humans.

Scientific classification: Lizards belong to the order Squamata.

Turtle

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Turtle, reptile with a bony or leathery shell. Any shelled reptile can be called a turtle, but in North America people commonly use the word tortoise to designate members of a family of turtles that live entirely on land, reserving the word turtle for species that live in or near water.

The upper shell of the turtle, under which the head, limbs, and tail can be more or less completely withdrawn, is called the carapace. The lower shell, which encases the belly, is called the plastron. The carapace and plastron are joined together on a turtle’s left and right sides by bony structures called bridges. The inner layer of a turtle’s shell is composed of about 60 bones, including portions of the backbone and the ribs. For this reason, a turtle cannot crawl out of its shell.

Most turtles and tortoises have conspicuous eyes placed well forward on the upper sides of their heads. Turtle species that live most of their lives on land usually focus their eyes downward toward objects in front of them. Some water-living turtles, like snapping turtles and soft-shelled turtles, have eyes nearer the top of the head. These turtles can hide from predators and prey in shallow bodies of water, where they lie nearly entirely submerged except for their eyes and nostrils. Sea turtles have glands near their eyes that produce salty tears, ridding the turtles’ bodies of the excess salt that they take in from drinking seawater. When a sea turtle is in the water, its tears are immediately washed away, but when these turtles arrive on land, they look as though they are crying.

Turtles use their jaws to cut and handle food. Instead of teeth, a turtle’s upper and lower jaws are covered by horny ridges, similar to a bird’s beak. Meat-eating turtles commonly have knife-sharp ridges for slicing through their prey. Plant-eating turtles often have ridges with serrated edges that help them cut through tough plants. Turtles use their tongues in swallowing food, but unlike many other reptiles, such as chameleons, they cannot stick out their tongues to capture food.

Scientific classification: Turtles make up the order Testudines in the class Reptilia. Hidden-necked turtles make up the suborder Cryptodira, and side-necked turtles comprise the suborder Pleurodira.

Reptiles

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Reptile, animal with tough, dry skin covered with horny scales. Some of the most widespread living reptiles are turtles, lizards, snakes, crocodiles, and alligators. Reptiles are vertebrates—animals that have a backbone. While they share characteristics common to other vertebrates—fish, amphibians, birds, and mammals—reptiles display a unique combination of characteristics that distinguishes them from other vertebrates. Like amphibians, modern reptiles are cold-blooded, or ectothermic. This means that they are unable to produce their own body heat, so they rely on the sun for warmth, and much of their behavior is directed toward regulating their body temperature. Like birds, most reptiles hatch from eggs that are laid on land, covered by a protective shell. Reptiles breathe air with lungs, as do most mature amphibians and all birds and mammals. And like amphibians and mammals, most reptiles, with the exception of turtles, have teeth. Reptile skin, with its tough, horny scales, is unique in the animal world. It is neither moist and permeable, like that of amphibians, nor feathered, like that of birds, nor covered with hair, like that of mammals.

TYPES OF REPTILES:
• Turtles and Tortoises
• Lizards
• Worm Lizards
• Snakes
• Crocodilians
• Tuatara

Scientific classification: Reptiles make up the class Reptilia, which is divided into four orders: Testudines, which contains turtles, terrapins, and tortoises; Squamata, which contains lizards, worm lizards, and snakes; Crocodilia, which contains crocodiles, alligators, caimans, and gavials; and Rhynchocephalia, which contains two species of tuatara.

Frog

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Frog (animal), small, tailless animal with a squat body and long, powerful hind legs adapted for jumping. Frogs have large, bulging eyes and moist skin. They typically live on land but spend part of their time in the water. Most frogs develop from small, fishlike larvae called tadpoles or pollywogs that live in water. This life divided between water and land is typical of amphibians, a group of related animals that includes toads, newts, and salamanders as well as frogs.

Frog Life Cycle
Most frogs have a life cycle with two distinct stages, typically living in water as young and on land as adults. Adult frogs lay large numbers of eggs in water or other moist places (A). The eggs hatch into small, fishlike larvae called tadpoles (B), which grow larger as they feed on algae and bits of plant material in the water (C). As it begins metamorphosis, or change into the adult body form, the tadpole grows hind limbs (D). After both pairs of limbs are complete and the animal has exchanged its gills for lungs, the young frog crawls out on land (E). The frog resorbs the rest of its tail and continues to grow until it reaches its adult body size (F).

Becoming a frog , the legless tadpoles that hatch from a floating mass of frog eggs are the animal’s fishlike larval stage. Part of a true metamorphosis, they have gills and a tail, both of which disappear as the tadpole feeds and grows. When limbs and air-breathing lungs develop, the young frog, now a miniature replica of its parents, emerges from water to land.

Scientific classification: Frogs are members of the order Anura in the class Amphibia. The bullfrog and the West African goliath frog are members of the family Ranidae and are classified as Rana catesbeiana and Conraua goliath, respectively. Poison dart frogs comprise several genera of the family Dendrobatidae. The African clawed frog belongs to the family Pipidae and is classified as Xenopus laevis. Marsupial frogs are members of the genus Gastrotheca in the family Hylidae. The extinct gastric brooding frog, Rheobatrachus silus, is classified in the family Myobatrachidae. Eleutherodactylus is a genus of frogs in the family Leptodactylidae. The family Bufonidae includes 380 species of toads, including the African toad, which is a member of the genus Nectophrynoides. Darwin’s frog is in the family Rhinodermatidae and is classified as Rhinoderma darwini.

Amphibian

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Amphibian, animal with moist, hairless skin through which water can pass in and out. Nearly all amphibians live the first part of their lives in water and the second part on land—a double life reflected in the name amphibian, which comes from the Greek words amphi, meaning “both,” and bios, meaning “life.” Amphibians were the first animals with backbones to adapt to life on land. They are the ancestors of reptiles, which in turn gave rise to mammals and birds.

Scientists recognize more than 4,000 species of amphibians, all of which are members of one of three main groups: frogs and toads, salamanders, or caecilians. Frogs and toads are the most abundant of all amphibians, numbering more than 3,500 species. Frogs have smooth skin and long limbs. Toads, in contrast, have warty skin and short limbs.

There are about 360 known species in the salamander group, which also includes newts and mud puppies. Members of this group have long, slender bodies ending in tails. Some salamanders live entirely on land, whereas others never leave the water, and still others spend some time in the water and some on land. Caecilians, with about 160 species, are the rarest of amphibians. They have no limbs and look much like earthworms. Most live underground and spend their time burrowing in the soil, but a few are aquatic.

Scientific classification: Amphibians are the only members of the class Amphibia, which contains three living orders. Salamanders, a group that includes newts and mud puppies, make up the order Caudata; frogs and toads make up the order Anura, and caecilians make up the order Gymnophiona.

Fish

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Fish, diverse group of animals that live and breathe in water. All fishes are vertebrates (animals with backbones) with gills for breathing. Most fish have fins for swimming, scales for protection, and a streamlined body for moving easily through the water.

Fishes may be divided into two distinct groups, jawless fish and jawed fish. The jawless fish are represented by two families of distantly related eel-like fish, the hagfish and the lampreys. Both fishes have tongues equipped with numerous small teeth and lack paired fins and a bony skeleton. Although these two families include only a handful of living species, the fossil record shows they were once a highly diverse group that also included fish whose head and trunk were covered with a hard bony shell. Hagfish are the vultures of the abyss, feeding on carcasses of dead fish and other animals. Lampreys, in contrast, feed on live fish by attaching their sucking disk to their host and rasping away tissue with their toothed tongue.

The jawed fish may also be separated into two major groups: bony fish, which have skeletons made of rigid bone, and cartilaginous fish, which have skeletons made of elastic cartilage. There are nearly 1000 species of cartilaginous fish, including sharks, rays, and chimaeras, or ratfish. Sharks and rays live in relatively shallow ocean waters and occasionally freshwater, while chimaeras are found only in the ocean, mostly in deep water. Sharks have an age-old reputation for savagery, but only a few of the approximately 370 species deserve this reputation. Most sharks, like the spiny dogfish, are predators of small fish and invertebrates, while the largest, such as megamouths, whale sharks, and basking sharks, feed by filtering tiny invertebrates from the water. The nearly 200 species of rays are essentially sharks flattened like a pancake that have adapted to life on the ocean floor.

The bony fishes encompass by far the largest diversity of fish, with about 24,000 species inhabiting nearly every body of water on the earth. They are divided into two groups—the lobe-finned fish and the ray-finned fish. Lobe-finned fishes include the lungfish, a small group of primitive air-breathing fish, and the coelacanth, the single living species of a group long thought to be extinct.

The ray-finned fishes are divided into two major groups, the primitive sturgeons and paddlefish, and the more evolved new-finned fishes. Most of the common and well-known fish species are new-finned fish, including the herrings, which support one of the largest fisheries in the world, and the eels, which are found in nearly all marine habitats. Other new-finned fishes include the ostariophysans—minnows, characins, and catfish—which inhabit the freshwaters of the tropics and surrounding areas. Salmon have adapted to the coasts of northern oceans by living part of their lives in freshwater and part in the ocean. There are over 9000 species of perch, including tunas, jacks, billfishes, sunfishes, and darters, making it the largest vertebrate order. Perches and their relatives are the dominant fishes in tropical marine waters. Closely related to the perches are the flatfish, which look and swim like normal fish when young, only to lay on one side of their body as adults after one eye migrates to the “top” side.

Scientific classification: Fishes are classified differently by different zoologists. Some of the classifications are very complex and divide fishes into more than 100 orders and suborders. In the most generally used system, the subphylum Vertebrata is divided into two superclasses: Agnatha, which includes the lamprey and other fishes without jaws; and Gnathostomata, which includes the fishes with hinged jaws. The latter are further divided into the class Chondrichthyes, the cartilaginous fishes such as the sharks, rays, and chimaeras, and the class Osteichthyes, the bony fishes.

The bony fishes are made up of the subclass Sarcopterygii, lobe-finned fishes, and the subclass Actinopterygii, ray-finned (or spiny-finned) fishes. The recent ray fins consist of two groups, the Chrondrostei and the Neopterygii, which includes the large division Teleostei or modern bony fishes.

Vertebrata

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Vertebrate, animal with a backbone, or spinal column, made of interlocking units called vertebrae. This strong but flexible structure supports the body and anchors the limbs, and it also protects the nerves of the spinal cord. Vertebrates include fish, amphibians, and reptiles, as well as birds and mammals. In all vertebrates, the spinal column forms part of a complete internal skeleton. Unlike the hard external skeleton covering an insect, which is periodically shed as the insect grows, a vertebrate’s internal skeleton can grow gradually along with the rest of the body.

There are over 40,000 species of vertebrates, which scientists classify into five groups: (1) fish, (2) amphibians, (3) reptiles, (4) birds, and (5) mammals. Scientists divide fish into three groups based on their anatomy: jawless fish, cartilaginous fish, and bony fish. The other vertebrate groups are made up of tetrapods, which have lungs and generally live on land.

Vertebrate

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Vertebrate, animal with a backbone, or spinal column, made of interlocking units called vertebrae. This strong but flexible structure supports the body and anchors the limbs, and it also protects the nerves of the spinal cord. Vertebrates include fish, amphibians, and reptiles, as well as birds and mammals. In all vertebrates, the spinal column forms part of a complete internal skeleton. Unlike the hard external skeleton covering an insect, which is periodically shed as the insect grows, a vertebrate’s internal skeleton can grow gradually along with the rest of the body.

Vertebrates make up only about 2 percent of the animal species, and they belong to just 1 of more than 30 phyla, or overall groups, in the animal kingdom. Despite this, vertebrates occupy a dominant position in almost all habitats and are by far the most familiar animals. When asked to name an animal at random, most people identify a type of vertebrate.

There are several reasons why vertebrates are so successful and so noticeable. One has to do with their size. Invertebrates—that is, animals without backbones, such as worms, shellfish, and insects—tend to be small and slow moving. This is because they lack effective ways to support a large body and the muscles needed to power it. Vertebrates, on the other hand, have evolved a much more versatile support system. Their skeletons can be adapted for use in many different ways and work just as well in an animal weighing 4 tons as in one weighing 113 g (4 oz). As a result, vertebrates have been able to develop bigger, faster bodies than invertebrates.

Vertebrates also have highly developed nervous systems. With the help of specialized nerve fibers, they can react very quickly to changes in their surroundings, giving them a competitive edge.

See Types of Vertebrates

Animals

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Animals are multicellular organisms, a characteristic they share with plants and many fungi. But they differ from plants and fungi in several important ways. Foremost among these is the way they obtain energy. Plants obtain energy directly from sunlight through the process of photosynthesis, and they use this energy to build up organic matter from simple raw materials. Animals, on the other hand, eat other living things or their dead remains. They then digest this food to release the energy that it contains. Fungi also take in food, but instead of digesting it internally as animals do, they digest it before they absorb it.

Most animals start life as a single fertilized cell, which divides many times to produce the thousands or millions of cells needed to form a functioning body. During this process, groups of cells develop different characteristics and arrange themselves in tissues that carry out specialized functions. Epithelial tissue covers the body's inner and outer surfaces, while connective tissue binds it together and provides support. Nervous tissue conducts the signals that coordinate the body (see Nervous System), and muscle tissue–which makes up over two-thirds of the body mass of some animals–contracts to make the body move. This mobility, coupled with rapid responses to opportunities and hazards, is one feature that distinguishes animals from other forms of life.

Some kinds of animal movement, such as the slow progress of a limpet as it creeps across rocks, are so slow that they are almost imperceptible. Others, such as the attacking dive of a peregrine falcon or the leap of a flea, are so fast that they are difficult or even impossible to follow. Many single-celled organisms can move, but in absolute terms, animals are by far the fastest-moving living things on earth.

Animal life spans vary from less than 3 weeks in some insects to over a century in giant tortoises. Some animals, such as sponges, mollusks, fish, and snakes, show indeterminate growth, which means that they continue to grow throughout life. Most, however, reach a pre-defined size at maturity, at which point their physical growth stops.

See also:
The Animal Kingdom

Classification of Animals -> Types of Vertebrates; Types of Invertebrates
Cold-blooded and warm-blooded animals

Tunicata

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Tunicate, common name for any member of a subphylum of primitive marine chordates. There are about 2000 known species. The larval stage is characterized by the presence of a notochord and a dorsal nerve cord, both of which are lacking in the adult. The adult is characterized by a layer of protective secretion called a tunic. Tunicates are common in such habitats as rocky shores but can also be found at great depths. Species known as sea squirts make up one class in the subphylum, and most tunicates belong to this class. Tunicates are important because they are an evolutionary link between invertebrates and vertebrates.

The larval stage, which generally resembles a tadpole, has a dorsal nerve cord protected by a notochord, a brain, gills, blood vessels, and a coelom. These features of tunicate larvae indicate that they are more closely related to the chordates than to the invertebrates. The free-swimming larva eventually attaches itself to a substrate and undergoes metamorphosis into the adult form, losing much of its resemblance to higher animals.

The adult is usually a sedentary animal possessing a complete digestive system, a heart and circulatory system, a gill net, and a reduced nervous system. It is covered by a tunic, which consists mainly of tunicin, a carbohydrate similar to cellulose. The vase-shaped animal has two siphons, one to allow water to enter the body cavity and the other to allow water to escape. The water passes through a filtering apparatus that captures small food particles and passes them to the stomach. The netlike branchial sac extracts oxygen from the water as it passes through. Most species are hermaphroditic (containing both male and female reproductive organs), but some free-living species, such as salps, reproduce alternately by sexual means and by asexual budding (see Alternation of Generations). Colonies may be formed by asexual reproduction, and some species form compound individuals that share a common excurrent siphon. One class of tiny, larvalike tunicates feed by means of a complicated mucous “house” that surrounds the body.

Scientific classification: Tunicates make up the subphylum Tunicata in the phylum Chordata. Sea squirts make up the class Ascidiacea, and salps make up the class Thaliacea. The larvalike tunicates that feed by means of a mucous “house” make up the class Larvacea.

Lancelet

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Lancelet, also called amphioxus, primitive fishlike animal that lacks a backbone but has many characteristics of vertebrates (animals with backbones). Many scientists believe that vertebrates may have evolved from an early ancestor similar to lancelets. Lancelets occur worldwide in shallow, marine environments, where they burrow into loose gravel or sand, leaving only their mouths protruding. Some Asian people consider lancelets a great delicacy, and the animal is commercially harvested in China.

Lancelets grow to a length of about 5 cm (2 in). They have an eel-like body shape with a well-defined mouth and tail. Most are semitransparent. Lancelets share a number of features in common with vertebrates, including a dorsal nerve cord that is supported by a stiff rod known as the notochord—a forerunner of the backbone; a system of pharyngeal slits between the mouth and stomach, used to strain food particles from water; and a series of segmented, V-shaped muscles along the torso.

Unlike vertebrates, lancelets do not develop a true brain, cranial nerves, or sensory structures, such as eyes or ears. Lancelets do not have a heart but they have a circulatory system in which a large blood vessel pulsates to move oxygenated blood to various organs in the body. Veins return blood to the gills, where it is replenished with oxygen. The sexes of lancelets are distinct—the sex organs occur in pairs along the body and produce gametes that are released into the water after the animal reaches maturity.

Lancelets have no hard body parts, such as bone, and as a result these animals only fossilize under special conditions. Fossils of animals believed to be lancelets found in south China and British Columbia date back to the early Cambrian Period, an interval of geologic history that began about 570 million years ago. These fossils may represent animals close to those from which vertebrates evolved.

Scientific classification: Lancelets make up the families Branchiostomatidae and Epigonichthyidae of the order Amphixi.

Chordata

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Chordate, common name for animals of the phylum Chordata, which includes vertebrates as well as some invertebrates that possess, at least for some time in their lives, a stiff rod called a notochord lying above the gut and beneath a single, hollow dorsal nerve cord. About 43,700 living species are known, making the chordates the third largest animal phylum. Three subphyla exist: Cephalochordata, the fishlike lancelets, with 25 species; Tunicata, the highly modified tunicates, with about 2000 species; and Vertebrata, animals with backbones made up of vertebrae (including fishes, amphibians, reptiles, birds, and mammals), with about 41,700 species. The closest relatives of the chordates, the acorn worms of the phylum Hemichordata, are sometimes treated as a chordate group but show only a trace of a dorsal nerve cord and a structure vaguely resembling a notochord. The best indication of their relationship to chordates is the presence of holes in the pharynx. In both hemichordates and lower chordates, the pharynx, with its gill slits, forms a complex structure that strains food particles from water.

Chaetognatha

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Arrowworm, common name for certain small, transparent, free-swimming marine animals. They are 1 to 8 cm (0.5 to 4 in) long, arrow-shaped, and streamlined, with one or two pairs of lateral fins and a caudal fin that propel the body forward in rapid, darting movements. The rounded head bears a set of bristles on each side, used in catching small animals. A retractable hood can be drawn over the bristles and mouth, which streamlines the head while swimming. Almost all arrowworms live in the open ocean waters. They occur in great numbers along coasts and continental shelves, where they constitute an important part of the food web as predators and as food for other animals. Arrowworms locate prey by detecting vibrations. All are hermaphrodites, containing both ovaries and testes, and some can fertilize themselves. The phylum is not very diverse, having only about 50 species in a few families. Arrowworms are quite unlike any other animals, but possibly may be related to echinoderms and chordates.

Scientific classification: Arrowworms make up the phylum Chaetognatha.

Brachiopoda

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Lampshell, common name for members of a phylum of small marine animals with two shells. Formerly classified in the same phylum as mollusks, lampshells differ from them in that the shells lie dorsally and ventrally instead of left and right, and the enclosed organism has an armlike appendage at each side of the mouth.

Lampshells were a dominant form of life in earliest geological times, but since the close of the Paleozoic Era, they have been steadily decreasing. Although nearly 4,700 genera are known, only about 81 of these are living today. Most living lampshells live at moderate depths, sometimes down to 450 m (1500 ft). Most are less than 2.5 cm (less than 1 in) across. The phylum is generally grouped into two classes: those that have hinged shell valves, and those that do not have hinges.

Scientific classification: Lampshells belong to the phylum Brachiopoda. Lampshells having hinges make up the class Articulata. Those without hinges make up the class Inarticulata.

Arthropoda

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Arthropod, animal with a hard, outer skeleton and a jointed body and limbs. Arthropods make up a phylum of invertebrates that includes insects, such as ants, beetles, and butterflies; crustaceans, such as lobsters, shrimps, and crabs; and arachnids, including scorpions, spiders, and ticks. In terms of sheer numbers and the variety of niches they fill, arthropods are the most successful animals on Earth. More than one million arthropod species have been identified—more than 20 times the number of known fish, amphibian, reptile, bird, and mammal species combined. This figure is considered a low estimate of the phylum's actual size because many arthropod species have yet to be discovered and documented. Some scientists suggest the number of arthropod species in tropical forests alone may approach six million to nine million.

Traditionally, living arthropods are classified among three subphyla: the Chelicerata, Crustacea, and Unirama. Trilobites, a fourth subphylum, flourished during the Cambrian and Ordovician periods of the Paleozoic Era (570 million to 435 million years ago) but became extinct by the mid-Permian Period (about 250 million years ago), for reasons that are not fully understood.

Chelicerata, named for their chelicerae, or specialized mouthparts, include scorpions, spiders, ticks, mites, and horseshoe crabs. These creatures have six pairs of appendages, one or two body regions, and lack wings and antennae. Most live on land, although a few are aquatic.

With a few exceptions, the Crustacea are aquatic, occupying both freshwater and saltwater niches. Familiar crustaceans include shrimps, lobsters, and crabs. All crustaceans have ten limbs, three body regions, and two pairs of antennae. Many of the smallest crustaceans are zooplankton—drifting or weak-swimming animals that form the base of most marine food webs.

The Unirama include centipedes, millipedes, and insects. Centipedes have wingless, multisegmented bodies, with one pair of legs on each body segment. The bodies of millipedes are also wingless and multisegmented but have two pairs of legs per segment. Insects have three pairs of legs, one pair of antennae, and may be wingless or have one or two pairs of wings. The majority of insects are land-dwellers, although some live in freshwater or marine environments.

Scientific classification: Arthropods make up the phylum Arthropoda, which is divided into three living subphyla: Chelicerata, Crustacea, and Unirama.

Annelida

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Annelid, common name for about 9000 species of wormlike invertebrate animals with well-developed segmentation. The three major classes of the annelid phylum are the bristle worms (about 5300 species), which are mainly marine and often luminescent; the oligochaetes (about 3100 species), which are mostly freshwater or inhabit the soil, such as the earthworm; and the leeches (about 300 species), which are mainly freshwater but may also be marine or terrestrial.

Although annelids are diverse in form, the bristle worms, which generally are considered the ancestral stock, can exemplify their structure. The elongate body is rounded in cross section, with a mouth (sometimes jawed) at one end and an anus at the other, and it exhibits bilateral symmetry. The body is made up of several similar units, or segments, separated externally by furrows and internally by septa (partitions). The segments generally bear parapodia (lobes) with setae (bristles) that are used in locomotion. The coelom (fluid-filled body cavity) provides a kind of structural support, so that the body is flexible. The gut is a straight tube and the nervous system fairly simple, with sense organs poorly developed. The head may bear eyes, feelers, or tentacles; a few bristle worms have highly developed eyes. Bristle worms grow by adding segments at the posterior end.

Oligochaetes have fewer setae and no parapodia. The body is streamlined and well adapted to burrowing, and the head does not have eyes or feelers. Leeches are flattened and can swim or crawl by looping movements; they usually lack setae.

Bristle worms generally have separate sexes and reproduce by releasing sperm and eggs into the water. By contrast, the basic pattern in earthworms and leeches is hermaphroditism, with cross-fertilization occurring internally. These animals produce cocoons, and some leeches care for the young.

Scientific classification: Annelids make up the phylum Annelida. Bristle worms make up the class Polychaeta, oligochaetes the class Oligochaeta, and leeches the class Hirudinea.

Acanthocephala

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Spiny-Headed Worm, a common name for members of a phylum of about 500 species of intestinal parasites that attach to a host by means of spines on an extensible proboscis. They lack a gut and circulatory system and absorb nutrients through the body wall. Adults have separate sexes and live in the intestines of vertebrates. Their eggs are shed with the host's feces and are eaten by invertebrates, into whose tissues the larvae burrow. When the invertebrates are eaten by vertebrates, the latter serve as new hosts. Spiny-headed worms do considerable damage to various fishes, birds, and mammals, including some domesticated animals.

Scientific classification: Spiny-headed worms make up the phylum Acanthocephala.

Animal Behavior

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Animal Behavior, the way different kinds of animals behave, which has fascinated inquiring minds since at least the time of Plato and Aristotle. Particularly intriguing has been the ability of simple creatures to perform complicated tasks—weave a web, build a nest, sing a song, find a home, or capture food—at just the right time with little or no instruction. Such behavior can be viewed from two quite different perspectives: Either animals learn everything they do (from “nurture”), or they know what to do instinctively (from “nature”). Neither extreme has proven to be correct.

Noninfectious Diseases of Animals

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Even if it were possible, a world without pathogens would not be disease-free. Many animal diseases are caused by noninfectious factors such as an animal's environment, genetics, and nutrition. Heatstroke, for example, occurs when an animal is forced to endure high temperatures without access to water, adequate ventilation, or suitable shade. A common scenario involves an animal that has been locked inside a car without air-conditioning during hot weather. Conversely, extreme cold can lead to hypothermia or frostbite. Other environmental hazards include the vast array of products humans use to eliminate pests and weeds from homes, farms, and gardens. For example, rodenticide, poison used to kill rats and mice, can cause fatal internal hemorrhaging in any animal that ingests this toxic substance. Improper use of flea powders, sprays, dips, and collars can also cause illness. Automobile antifreeze is another well-known poison. Its sweet taste appeals to some animals, such as cats and dogs, but consuming only a small amount can result in death. Many plant species are also toxic to animals. Some, such as pokeweed and yew, commonly grow in pastures and yards.

Poor feeding practices can lead to diseases such as nutritional secondary hyperparathyroidism, a condition involving the muscles and bones of dogs that is associated with an all-meat diet. Large, rapidly growing puppies that consume too many calories and too much calcium can develop hypertrophic osteodystrophy, a disease resulting in lameness. Cats need sufficient amounts of an essential amino acid called taurine in their diets. Without it, they may develop eye problems. Not enough iodine intake can cause a goiter, or enlargement of the thyroid gland, in cows, horses, and other animals.

Trauma is a leading cause of injury and premature death in animals, especially pets that are allowed to roam free outdoors. Many animals are hit by cars or bitten by other animals. Farm animals may be attacked by predators, or they may harm themselves on sharp fencing or discarded nails. Untreated wounds can become infected and cause permanent damage.

Hip dysplasia, a painful and debilitating skeletal condition, is a noninfectious disease caused in part by heredity. Certain defects of the heart or palate, the roof of the mouth, may also be inherited. Some animals are genetically predisposed to diseases such as generalized demodectic mange, a skin disease caused by mites and characterized by hair loss and scaling around the eyelids, mouth, and front legs.

An animal's immune system is designed to detect and eliminate invading organisms. Occasionally, however, it behaves as though the animal's own body were the attacker, and it destroys healthy tissue. Diseases caused by this response, known as autoimmune diseases, include pemphigus foliaceous, a skin disease of dogs, cats, and horses; and rheumatoid arthritis, a severe type of arthritis that involves inflammation of the joints. In the autoimmune disease hemolytic anemia, the animal's own red blood cells are destroyed by its immune system.

Cancer exists in all animals. It is classified as either benign—that is, relatively noninvasive and unlikely to return after treatment; or as malignant—that is, aggressive and likely to spread. Any organ or system can be affected, either directly or through metastasis—when cancer cells from one part of the body spread to other areas of the body. Some forms of cancer are more widespread in animals of a particular breed, age, or sex, and even individuals of a specific color. For example, cancer of the mammary gland occurs more often in female animals, while melanoma, or skin cancer, is the most frequent tumor of elderly gray horses, and lymphosarcomas, tumors of the lymph nodes, are the most common type of specific tumor in cats. The study of cancer, known as oncology, is a growing field in veterinary medicine.

Prevention and Treatment of Animal Diseases

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Controlling the spread of infectious animal diseases begins with isolating, or quarantining, animals with threatening infections, such as salmonella, to prevent further transmission. Many bacterial diseases can be treated with various antibiotics, such as penicillin and streptomycin. But as with all disease, prevention is more important than treatment, and a major activity for veterinarians is immunization of animals. Immunization commonly involves an injection of a weakened or killed pathogen for a specific disease that encourages the immune system to fight off infection. Many infectious diseases, including rabies, canine distemper, feline leukemia, anthrax, and brucellosis, can be prevented by immunization. In the case of severe outbreaks of infectious disease, public health officials may work with animal owners to destroy large groups of animals.

Transmission of animal diseases to humans is a constant concern of public health officials. To protect people from disease, veterinarians inspect food animals for wholesomeness; quarantine and examine animals brought into the United States from other countries; test animals for the presence of disease; and actively work to prevent and eradicate diseases that threaten human health.

Diseases of Animals

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Diseases of Animals are disorders that influence an animal's health and ability to function. Animal diseases are of great concern to humans for several reasons. Diseases can reduce the productivity of animals used to produce food, such as hens and dairy cows. Animals that are raised as food, such as pigs and beef cattle, that become ill may affect the economic well-being of many industries. Some animal diseases can be transmitted to humans, and control of these types of diseases, known as zoonoses, is vital to public health. In the wild, animal populations reduced by disease can upset the ecological balance of an area. And, in the case of pets, prevention and treatment of animal diseases helps pets live long and healthy lives, enhancing the companionship shared by a pet and its human owner.

Animal diseases are characterized as infectious and noninfectious. Infectious diseases are caused by an agent, such as bacteria or a virus, that penetrates the body's natural defense mechanisms, while noninfectious diseases are caused by factors such as diet, environment, injury, and heredity. Sometimes the cause of a disease is unknown. An animal may also experience one disease or a combination of diseases at any one time.

To identify a disease, a veterinarian (a doctor who treats animals) first determines the animal's signalment—its species, breed, age, and sex. This information helps to identify a disease because some diseases are more prevalent in certain species, or a disease may preferentially affect one sex or age group. The veterinarian then gathers a complete history of the animal and its problem. This history includes the symptoms the animal is displaying and when they first appeared, as well as whether the animal has been exposed to something new in its surroundings or to other animals. The veterinarian gives the animal a thorough physical examination, which may include measuring its body temperature, listening to its heart, checking its pulse, and feeling its abdomen and lymph nodes. The veterinarian then creates a list of possible diseases that may be making the animal sick. The list may be narrowed by running diagnostic tests such as X rays, electrocardiograms, blood analyses, and bacterial or fungal cultures. Once the disease is identified, the doctor develops a treatment plan for the animal (see Veterinary Medicine).

See INFECTIOUS DISEASES: Bacterial Diseases; Viral Diseases; Fungal Diseases; Parasitic Infections; Prion Diseases

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