Kids Research Express

. 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.

. 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 co

. 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 see

. 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

. 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

. 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

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 t

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

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 f

. 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.

. 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.

. 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

. 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.

. 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 parasit

. 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 deve

. 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

. 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 lo

. 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 ro

. 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 knot

. 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, slu gs, 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

. 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.

. 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 classificati

. 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 dig

. 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 t

. 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

. 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, inges

. 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

. 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. Th

. 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

. 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 th

. 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 an

. 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 h

. 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 climate

. 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 d

. 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, woundi