Tick

Tick, common name for members of a group of large mitelike arachnids parasitic on mammals, birds, and reptiles. All ticks are bloodsucking parasites. Ticks are found in most parts of the world but are generally limited to those habitats frequented by their hosts—namely, woods, tall grass, and shrubby vegetation—where they climb onto plants and wait to jump on a passing host.

Ticks are actually a specialized group of mites and share many features with other mites. In general, they are larger than most mites, ranging from about 0.2 to 0.6 cm (about 0.08 to 0.24 in) in length, although females may be 1 cm (0.4 in) or more in diameter when fully engorged with blood. The adult tick has a mitelike body with a tough skin and four pairs of clawed legs; tick larvae have only three pairs of legs. The mouthparts consist of a paired anchoring organ, or rostrum, covered with backward-curving hooks and equivalent to the pedipalps of other arachnids; and a pair of sharp mandibles that move back and forth in two longitudinal channels on the rostrum.

Ticks are divided into two families: hard ticks and soft ticks. In hard ticks, the mouthparts are visible from above. Hard ticks are parasites primarily of mammals but are also found on birds and reptiles. The nymphs may feed on a different host species in each developmental stage; in each stage, the nymph feeds only once. The adult female lays a single large batch of eggs after her final meal. The American dog tick is perhaps the most familiar North American hard tick. Another important species is the deer tick, which is known to transmit Lyme disease to humans.

In soft ticks, the mouthparts are hidden underneath the body. In general, soft ticks are parasites of birds, but some feed on other hosts. Usually all the developmental stages feed on a single host species. Each stage may feed many times over a period of at least several days, taking refuge in nearby crevices or under rocks when not feeding. The adult female soft tick lays relatively few eggs over an extended period. The relapsing-fever tick is a soft tick that occasionally bites humans.

Cytology

Cytology

Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the problems of heredity.

Cytology, branch of biology concerned with the study of the structure and function of cells as individual units, supplementing histology, which deals with cells as components of tissues. Cytology is concerned with the structure and activities of the various parts of the cell and cell membrane; the mechanism of cell division; the development of sex cells, fertilization, and the formation of the embryo; cell derangements such as those occurring in cancer; cellular immunity; and the problems of heredity.

Genetics

Genetics, study of the function and behavior of genes. Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans. Offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the color of a flower’s petals, the markings on a butterfly’s wings, or such human behavioral traits as personality or musical talent. Geneticists seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. Geneticists also study how tiny variations in genes can disrupt an organism’s development or cause disease. Increasingly, modern genetics involves genetic engineering, a technique used by scientists to manipulate genes. Genetic engineering has produced many advances in medicine and industry, but the potential for abuse of this technique has also presented society with many ethical and legal controversies.

Genetic information is encoded and transmitted from generation to generation in deoxyribonucleic acid (DNA). DNA is a coiled molecule organized into structures called chromosomes within cells. Segments along the length of a DNA molecule form genes. Genes direct the synthesis of proteins, the molecular laborers that carry out all life-supporting activities in the cell. Although all humans share the same set of genes, individuals can inherit different forms of a given gene, making each person genetically unique.

Parasite

Parasite, organism that lives in or on a second organism, called a host, usually causing it some harm. A parasite is generally smaller than the host and of a different species. Parasites are dependent on the host for some or all of their nourishment. For example, a tapeworm, a flattened worm that lives in the gastrointestinal tract of mammals, lacks an intestine of its own and must absorb predigested food from the intestine of its host. This food is the tapeworm’s only energy source for growth and reproduction. Parasitism affects most life forms, from bacteria infected by the viruses known as bacteriophages, to humans, who are subject to more than 100 parasites known to cause disease.

See also:
Types and Forms of Parasites
Parasites and Host Relationships
Life Cyle of Parasites
Parasites of Humans
Parasites of Animals
Parasites of Plants
Parasitology

Biodiversity

Biodiversity
Biodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, and microbial organisms living on Earth and the variety of habitats in which they live. Scientists estimate that upwards of 10 million—and some suggest more than 100 million—different species inhabit the Earth. Each species is adapted to its unique niche in the environment, from the peaks of mountains to the depths of deep-sea hydrothermal vents, and from polar ice caps to tropical rain forests.

Biodiversity underlies everything from food production to medical research. Humans the world over use at least 40,000 species of plants and animals on a daily basis. Many people around the world still depend on wild species for some or all of their food, shelter, and clothing. All of our domesticated plants and animals came from wild-living ancestral species. Close to 40 percent of the pharmaceuticals used in the United States are either based on or synthesized from natural compounds found in plants, animals, or microorganisms.

related articles:

• evolution
• extinction
• animals
• ecosystems
• plants

Extinction

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Extinction (biology), the end of existence of a group of organisms, caused by their inability to adapt to changing environmental conditions. Extinction affects individual species—that is, groups of interbreeding organisms—as well as collections of related species, such as members of the same family, order, or class (see Classification). The dodo, for example, a species of flightless pigeon formerly living on the island of Mauritius, became extinct in 1665. About 10,000 to 12,000 years ago, the most of the woolly mammoths and the last of the mastodons, both members of the elephant family, died. And about 245 million years ago at the end of the Paleozoic Era, an entire class of primitive marine animals called trilobites disappeared forever.

Fossils, the remains of prehistoric plants and animals buried and preserved in sedimentary rock or trapped in amber or other deposits of ancient organic matter, provide a record of the history of life on Earth. Scientists who study this fossil record, called paleontologists, have learned that extinction is a natural and ongoing phenomenon. In fact, of the hundreds of millions of species that have lived on Earth over the past 3.8 billion years, more than 99 percent are already extinct. Some of this happens as the natural result of competition between species and is known as natural selection. According to natural selection, living things must compete for food and space. They must evade the ravages of predators and disease while dealing with unpredictable shifts in their environment. Those species incapable of adapting are faced with imminent extinction. This constant rate of extinction, sometimes called background extinction, is like a slowly ticking clock. First one species, then another becomes extinct, and new species appear almost at random as geological time goes by. Normal rates of background extinction are usually about five families of organisms lost per million years.


related articles:
mass extinctions
role of mass extinction in evolution

Hydrozoa

Hydrozoa

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.

Cnidarians

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Cnidarians, also known as coelenterates, diverse group of aquatic, invertebrate animals armed with microscopic stinging structures. Cnidarians make up the phylum Cnidaria, which encompasses more than 9,000 species, including corals, hydras, jellyfishes, Portuguese man-of-war, and sea anemones. Cnidarians live in all oceans, and a few species inhabit fresh water.

Cnidarians have many shapes and they range in size from microscopic hydrozoans to jellyfishes that are 2 m (7 ft) in diameter with tentacles 30 m (100 ft) long. Although they have various physical characteristics, all cnidarians exhibit radial symmetry—that is, similar body parts radiate from a central mouth. Six to ten tentacles surround a cnidarian’s mouth to aid in the capture and ingestion of the animals they feed on.

Cnidarians have a saclike body with a single mouth opening. The body wall is composed of two sheets of cells—an inner layer (the endoderm) and an outer layer (the ectoderm). A gelatinous mesoglea layer holds these two cell layers together. Cnidarians are invertebrates (animals that lack a backbone), but the ectoderm of some cnidarians, including hard corals and some hydrozoans, may form a skeleton-like structure externally. The ectoderm of other cnidarians, such as some soft corals, forms an internal skeleton-like structure. The ectoderm and endoderm layers contain contractile fibers that enable the animal to move about. Invertebrate zoologists believe these fibers are primitive versions of the muscle cells found in more complex animals.

Cnidarians lack internal organs and they do not have digestive, circulatory, or respiratory systems. Secretions from endoderm cells digest food within the central body cavity and endoderm cells also distribute nutrients and dissolved oxygen to all parts of the body. Lacking an anus, cnidarians discharge waste matter through the mouth opening.

Reproduction in cnidarians varies among the different species. They may reproduce by means of asexual reproduction, sexual reproduction, or both. Polyps generally perform asexual reproduction by budding, in which an outgrowth from the body wall separates to form a new polyp or medusa. Medusae primarily reproduce sexually—they produce gametes (sex cells), and a gamete (sperm) from a male medusa fuses with a gamete (egg) from a female medusa to form a zygote. The zygote develops into a larva, which in turn develops into a polyp or medusa. The medusae of some cnidarians may also form polyps by budding.

Scientists divide cnidarians into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. They base this division partly on whether the polyp or medusa is more conspicuous during an animal’s life cycle.

Scientific classification: The phylum Cnidaria is made up of the classes Hydrozoa (predominately polyps), Scyphozoa (primarily medusae), Cubozoa (primarily medusae), and Anthozoa (polyps only).

See Types of Cnidarians; Polyp and Medusa Structures

Polyp and Medusa Structures

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During the life cycle of cnidarians they may form two types of body structures, the polyp and the medusa. Some cnidarians alternate between polyp and medusa at different stages of their life cycles, some cnidarians live solely as polyps, and others only as medusae.

A polyp has a cylindrical shape. The mouth, surrounded by tentacles, is located at one end of the polyp, and the opposite end of the polyp typically attaches to a rock or other object on the sea bottom. Polyps may be solitary, as in some types of hydras, or they may attach to other polyps to form a colony, as corals do. In some cnidarians, such as those from the genus Obelia, the polyps of a single colony may perform specialized functions. Some polyps in a colony capture food, others reproduce, and others protect the colony.

The medusa body resembles a saucer or umbrella. The mouth is located in the center of the undersurface of the saucer-like body, surrounded by tentacles. Medusae are solitary and most swim freely in the water. The gelatinous mesoglea layer in medusae is quite thick, which is why cnidarians with the medusae body form are commonly referred to as jellyfish.

related articles:

• Cnidarians
• Nematocysts
• Reproduction in Cnidarians
• Types of Cnidarians

Nematocysts

Nematocysts

The name cnidarian derives from the Greek word knidos, meaning “nettle,” referring to the microscopic stinging structures known as nematocysts found on cnidarian tentacles. A cnidarian will stun a prey animal with its nematocysts and then use its tentacles to bring the prey to its mouth to swallow.

Each nematocyst contains a coiled tubule that shoots out like a harpoon with explosive force. There are about 30 kinds of nematocysts that work in different ways to stun prey. The tubules of some nematocysts wrap around prey. The tubules of other nematocysts stick to prey, while other tubules pierce the surface of small animals. The nematocysts of some cnidarians contain poison that can paralyze or kill prey.

related topics:

• Cnidarians
• Polyp and Medusa Structures
• Reproduction in Cnidarians
• Types of Cnidarians

Reproduction in cnidarians

Reproduction in cnidarians

Reproduction in cnidarians varies among the different species. They may reproduce by means of asexual reproduction, sexual reproduction, or both. Polyps generally perform asexual reproduction by budding, in which an outgrowth from the body wall separates to form a new polyp or medusa. Medusae primarily reproduce sexually—they produce gametes (sex cells), and a gamete (sperm) from a male medusa fuses with a gamete (egg) from a female medusa to form a zygote. The zygote develops into a larva, which in turn develops into a polyp or medusa. The medusae of some cnidarians may also form polyps by budding.

The reproductive life cycle of a typical jellyfish illustrates both asexual and sexual reproduction. Males release sperm and females release eggs into the water. When an egg and sperm fuse during sexual reproduction, a larva develops that attaches to a rock or other object and develops into a polyp. In a type of asexual reproduction, the polyp divides to form a colony of polyps that resembles a stack of saucers. Each saucer in the stack develops tentacles and swims away from the colony as a new medusa, and the reproductive cycle repeats.

related topics:

• Cnidarians
• Polyp and Medusa Structures
• Nematocysts
• Types of Cnidarians

Types of Cnidarians

Scientists divide cnidarians into four classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa. They base this division partly on whether the polyp or medusa is more conspicuous during an animal’s life cycle.

Hydrozoa
In Hydrozoa, the polyp phase dominates in the animal’s life cycle. Most hydrozoan polyps reproduce by budding to form a polyp colony that fastens to solid objects such as rocks and pilings. Some hydrozoan polyps also bud to form a medusa, which is generally small and lives only a short time. This class comprises about 3,100 species, including the freshwater hydra (which lacks a medusa stage), the Portuguese man-of-war, and fire coral.

Scyphozoa
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.

Cubozoa
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.

Anthozoa
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).

Invertebrate

Invertebrate, any animal lacking a backbone. Invertebrates are by far the most numerous animals on Earth. Nearly 2 million species have been identified to date. These 2 million species make up about 98 percent of all the animals identified in the entire animal kingdom. Some scientists believe that the true number of invertebrate species may be as high as 100 million and that the work of identifying and classifying invertebrate life has only just begun.

Invertebrates live in a vast range of habitats, from forests and deserts to caves and seabed mud. In oceans and lakes they form part of the plankton—an immense array of miniature living organisms that drift in the surface currents. Invertebrates are also found in the soil beneath our feet and in the air above our heads. Some are powerful fliers, using wings to propel themselves, but others, particularly the smallest invertebrates, float on the slightest breeze. These tiny invertebrates form clouds of aerial plankton that drift unseen through the skies.

Although the majority of invertebrates are small, a few reach impressive sizes. The true heavyweights of the invertebrate world are giant squid, which can be over 18 m (59 ft) long and can weigh more than 2,000 kg (4,000 lb). The longest are ribbon worms, also known as nemerteans, whose pencil-thin bodies can grow up to 55 m (180 ft) from head to tail. At the other end of the size scale, animals called rotifers rank among the smallest invertebrates of all. Some species may reach 3 mm (0.12 in) in size, but most are less than 0.001 mm (0.00004 in), smaller than the largest bacteria.

See Types of Invertebrates; Reproduction and Life Cycle

Invertebrates: Reproduction and Life Cycle

Invertebrates: Reproduction and Life Cycle

Invertebrates display a wide variety of methods of reproduction. Some invertebrates reproduce by asexual reproduction, in which all offspring are genetically identical to the parent. Asexual reproduction methods include fragmentation, in which animals divide into two or more offspring, and budding, in which animals sprout buds that break away to take up life on their own. The majority of invertebrates reproduce sexually. The genes from two parents recombine to produce genetically unique individuals. For most invertebrates, sexual reproduction involves laying eggs. With a few exceptions, such as scorpions and spiders, most invertebrates abandon their eggs as soon as they are laid, leaving them to develop on their own.

When invertebrate eggs hatch, the animals that emerge often look nothing like their parents. Some are so different that, in the past, zoologists mistook them for entirely new species. Young like this are known as larvae. As they grow up, larvae change shape, a process known as metamorphosis. A larval stage enables invertebrates to live in different habitats at different stages of their lives. For example, adult mussels live fastened to rocks, but their larvae live floating among plankton. By having larvae that drift with the currents, mussels are able to disperse and find homes with new food sources for their adult life.

The change from larva to adult is quite gradual in many invertebrates, such as crabs and lobsters, but in insects it can be much more abrupt. Caterpillars, the larvae of butterflies and moths, often live for several months, but they take just a few days to turn into adults. During the transition stage, known as the pupa, the caterpillar’s body is broken down and reassembled, forming an adult insect that is ready to breed.

Most invertebrates are short-lived animals, but slow-growing species often break this rule. Wood-boring beetles can live well into their teens, while queen termites can live 40 years or more. But in the invertebrate world, the real veterans live in the sea. Growth lines on bivalve shells suggest that some clams can live to be 200 years old or more. A similar age has been claimed for pogonophoran worms living around hydrothermal vents in the darkness of the deep seafloor.

Types of Invertebrates

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Zoologists (scientists who study animals) classify invertebrates into about 30 major groups, known as phyla. These phyla vary enormously in the number of species they contain. Arthropods (phylum Arthropoda) are the invertebrate phylum with the most species—more than one million known species and countless more awaiting discovery. The mollusks (phylum Mollusca) make up the second largest group of invertebrates, with at least 50,000 species. Among the simplest invertebrates are the sponges (phylum Porifera). Other major invertebrate phyla include the cnidarians (phylum Cnidaria), echinoderms (phylum Echinodermata), and several different groups of worms, including flatworms (phylum Platyhelminthes), roundworms (phylum Nematoda), and annelids (phylum Annelida).

Invertebrates Phylum:

Placozoa -> Microscopic marine animal. Flattened body composed of two outer layers of flagellated cells enclosing loose cells. Reproduces asexually and possibly sexually. – Examples: Single species identified as Trichoplax adherens.

Porifera -> Simple, multicellular animals with tissues but no distinct organs. Commonly known as sponges, they typically attach to rocks, shells, or coral. Most sponges have an irregular shape supported by a skeleton composed of calcareous crystals, silicon spicules, or spongin fibers. Most sponges have an internal water canal system that moves water through the body, providing a constant supply of food particles and oxygen to all cells and removing wastes. Sponges reproduce sexually. They regenerate lost or injured body parts. – Examples: Sponges

Cnidaria -> Aquatic radially symmetrical animals with tentacles encircling the mouth at one end of the body. Cnidarians appear in two forms during their life cycle, the sessile, cylindrical polyp and the free-swimming medusa that looks like a jellyfish. Most feed on zooplankton, although some eat larger invertebrates. Cnidarians use tentacles to capture prey, immobilizing the prey with stinging cells called nematocysts. Cnidarians reproduce both asexually (by budding) and sexually. Some species are hermaphroditic, with both eggs and sperm produced in each individual. Most regenerate lost or injured body parts. – Examples: Coral, hydra, jellyfish, Portuguese man-of-war, sea anemone

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Phylum

Phylum

Phylum, in biology, major category, or taxon, of organisms with a common design or organization. This design is shared by all members of the phylum, even though structural details may differ greatly because of evolution. The assumption is made by biologists that all members of a phylum have a common ancestry.

A phylum is part of the hierarchy of classification of organisms. It is an arbitrary grouping; that is, it is developed from a combination of scientific observation, theorizing, and guesswork in an attempt to find order in the complexity of living and extinct life forms. The same is true of all classification levels above and below it except for species, which consist of organisms known to be capable, at least potentially, of interbreeding (see Species and Speciation).

related topics:

• animal phyla
• plant phyla

Evolution

Evolution
Evolution, in biology, complex process by which the characteristics of living organisms change over many generations as traits are passed from one generation to the next. The science of evolution seeks to understand the biological forces that caused ancient organisms to develop into the tremendous and ever-changing variety of life seen on Earth today. It addresses how, over the course of time, various plant and animal species branch off to become entirely new species, and how different species are related through complicated family trees that span millions of years.

Evolution provides an essential framework for studying the ongoing history of life on Earth. A central, and historically controversial, component of evolutionary theory is that all living organisms, from microscopic bacteria to plants, insects, birds, and mammals, share a common ancestor. Species that are closely related share a recent common ancestor, while distantly related species have a common ancestor further in the past. The animal most closely related to humans, for example, is the chimpanzee. The common ancestor of humans and chimpanzees is believed to have lived approximately 6 million to 7 million years ago (see Human Evolution). On the other hand, an ancestor common to humans and reptiles lived some 300 million years ago. And the common ancestor to even more distantly related forms lived even further in the past. Evolutionary biologists attempt to determine the history of lineages as they diverge and how differences in characteristics developed over time.

Types of Invertebrates

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Arthropoda -> Largest and most diverse invertebrate phylum characterized by animals with jointed limbs, a segmented body, and an exoskeleton made of chitin. Arthropods are abundant and successful in almost all habitats. The exoskeleton is divided into plates that enhance flexibility and movement. Periodic molting of the exoskeleton permits growth. Arthropods have a complex brain and nervous system. Many arthropods have a compound eye made up of numerous light-sensitive parts. Reproduction is sexual. – Examples: Ants, beetles, butterflies, lobsters, shrimp, crabs, scorpions, spiders, ticks

Ectoprocta or Bryozoa -> Small, mostly marine animals that resemble simplified horseshoe worms, with a lophophore surrounding the mouth. They live in colonies, attaching to the sea bottom or seaweed. Bryozoans are hermaphroditic and reproduce asexually (by budding) and sexually. – Examples: Moss animals

Entoprocta or Kamptozoa -> Small, mostly marine animals with a globular body mounted on a stalk. A lophophore surrounds both the mouth and anus. Entoprocts live in colonies. They reproduce both asexually and sexually. – Examples: Urnatella, Pedicellina

Brachiopoda -> Marine animals that resemble clams except that their shells form on the top and bottom of the animal, while clam shells form on the left and right of the animal. The shell attaches to the ocean bottom, rocks, or other objects by means of a cordlike stalk. Brachiopods reproduce sexually. – Examples: Lamp shells

Echinodermata -> Marine animals distinguished by their radial symmetry in which the body can be divided into five parts arranged around a central axis. They have internal skeletons composed of calcareous ossicles with projecting spines that give the body surface a bumpy appearance. They use body appendages called processes for feeding and locomotion. Reproduction is sexual and some have a larval form. – Examples: Sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers

Cycliophora -> Discovered in 1995, these parasites live in the mouthparts of certain lobsters. They have a characteristic saclike body with a bell-shaped mouth structure called a buccal funnel. Only one species has been identified, and it displays alternation of generations, with both asexual and sexual components of the life cycle. – Example: Single species identified as Symbion pandora

Loricifera -> Marine sediment dwellers with a protective structure called a lorica, consisting of plates that surround the animal's trunk. The mouth and head retract into the lorica for protection. Reproduction is sexual and little is known about the life cycle, although a larval form has been identified. – Examples: Nanaloricus mysticus

Onychophora -> Terrestrial, caterpillar-like animals found only in the tropics and southern hemisphere. The soft body is covered by a flexible cuticle that periodically molts. The head region contains a pair of antennae and clawlike mandibles. They have from 14 to 43 pairs of legs, depending upon the species and gender. Reproduction is sexual. – Examples: Velvet worms

Chaetognatha -> Torpedo-shaped marine animals with fins that enable them to swim with rapid, dartlike movements as well as gliding and floating motions. Movable hooks on their heads are used to capture prey. These animals are hermaphrodites and reproduction is sexual. – Examples: Arrow worms

Hemichordata -> Simple, wormlike marine animals with a primitive notochord and a system of gills. They use a distinctive proboscis to capture food and also to aid in locomotion. Reproduction is sexual and some have a larval form that resembles the larvae of echinoderms. – Examples: Acorn worms

Types of Invertebrates

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Annelida -> Segmented worms with a muscular body wall used for burrowing. External hairs called setae aid in traction during burrowing. An internal coelom is divided into compartments by walls known as septum. The digestive system stretches from the mouth to the anus, differentiated into regions, each with a different function. Reproduction is sexual. – Examples: Lugworms, earthworms, leeches

Pogonophora -> Deep-sea worms that live in chitinous tubes attached to the ocean floor. Their long, slender body has a beard of tentacles at the head end. There is no mouth or digestive system and these animals absorb all nourishment through the body surface. They reproduce sexually. – Examples: Bead worms

Vestimentifera -> Giant deep-sea worms that live in chitinous tubes attached to the ocean floor. They derive nutrition using a specialized organ called a trophosome to digest sulfide-oxidizing bacteria. – Examples: Llamellibrachs

Sipuncula -> Marine worms with a saclike body and a long proboscis. These worms withdraw their narrow head into the fatter posterior portion. The head end bears tentacles used in burrowing and gathering food particles. Lacking a cardiovascular system, they use internal fluid to transfer oxygen and food to body tissues. They reproduce sexually and some have a larval form. -> Peanut worms

Echiura -> Plump marine worms that take shelter in sand burrows or rock crevices. They use a mucous net or a scoop-shaped proboscis to capture food particles. Reproduction is sexual. – Examples: Spoon worms

Priapulida -> Cucumber-shaped, marine worms with spiny heads. During movement the barrel-shaped proboscis withdraws into the trunk of the worm. Reproduction is sexual. – Examples: Priapulus

Tardigrada -> Microscopic animals with four pairs of stubby legs that live in marine and freshwater sediments and on the surface of mosses and lichens. They use sharp stylets protruding from their mouths to suck food from plant cells. These animals have a remarkable ability to withstand extreme dryness and low temperatures. Reproduction is sexual. – Examples: Water bears

Pentastomida or Linguatulida -> Parasitic worms that live in the lungs of snakes, crocodiles, and some mammals and birds, feeding on blood and tissue. The head bears four leglike claws and a snoutlike mouth. The body is covered by a cuticle that is molted during larval development. They reproduce sexually. – Examples: Tongue worms

Phoronida -> Cylindrical, marine worms that live in a chitinous tube embedded in sand or attached to rocks, shells, or other objects in shallow water. Protruding out of the tube is the animal's lophophore, a structure of ciliated tentacles arranged in a horseshoe shape, that is used for feeding. They have a U-shaped digestive tract. Adults are sedentary and larvae are free-swimming. Reproduction is asexual in at least one species, but most species reproduce sexually. – Examples: Horseshoe worms

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Types of Invertebrates

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Kinorhyncha or Echinodera -> Tiny worms with spiny bodies. An outer protective cuticle is segmented and articulated. Found in the muddy bottoms of coastal waters, they feed on microorganisms and organic particles by means of a sucking pharynx. Reproduction is sexual. Examples: Echinoderes, Condyloderes

Nematoda -> Commonly known as roundworms, these animals are one of the most diverse and geographically widespread invertebrate phyla. Free-living roundworms inhabit freshwater and marine habitats, as well as soil. Parasitic roundworms prey on both plants and animals, causing widespread agricultural damage and disease. Roundworms have long, cylindrical bodies with a mouth surrounded by lips and sensory papillae or bristles. Fluid in the body cavity distributes nutrients and oxygen—roundworms do not have special respiratory or circulatory systems. Roundworms prey on other invertebrates as well as diatoms, algae, and fungi. They reproduce sexually and larvae undergo at least four molts before reaching their adult size and shape. – Examples: Ascarids, vinegar eels, cyst nematodes, heartworms, hookworms

Nematomorpha -> Long, threadlike worms found in soil or freshwater, commonly known as horsehair worms. They have no distinct head. Larvae are parasitic on terrestrial arthropods, usually insects. Adults do not feed but depend entirely on nutrients obtained during the parasitic larval stage. Reproduction is sexual. – Examples: Nectoneme, gordian worms

Acanthocephala -> Worms characterized by the presence of retractable spiny hooks that attach to the intestinal walls of aquatic and terrestrial vertebrates. Lacking a digestive tract, these worms absorb nutrients through their body wall. Reproduction is sexual and the life cycle includes larval forms that are parasites of crustaceans or insects. – Examples: Spiny-headed worms

Gnathostomulida -> Elongated, ciliated worms that live in marine sand. These animals have a mouth structure with a combed plate and toothed jaws. Bacteria and fungi are scraped into the mouth by the comb and passed into the gut by snapping movements of the jaws. Hermaphroditic, these animals reproduce sexually. – Examples: Jaw worms

Mollusca -> Diverse animals found in water and on land. Most mollusks have a hard shell that protects a soft body, although in some mollusks the hard shell is missing or hardly visible. A feeding organ called a radula contains rows of teeth used to scrape food into the mouth. Enzymes in salivary glands partially digest food before it reaches the intestines. Reproduction is sexual and some mollusks have a larval form. – Examples: Chitons, oysters, snails, clams, squid

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Types of Invertebrates

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Ctenophora -> Jellyfish-like marine animals distinguished by eight rows of cilia that propel the body in swimming. They feed on other invertebrates using two retractable sticky tentacles to capture prey. All ctenophores are hermaphroditic and reproduce sexually. Many are luminescent. – Examples: Sea walnuts, comb jellies

Platyhelminthes -> Structurally simple worms with no anus or circulatory system. Known as flatworms, their flattened bodies enable internal tissues to be near the skin surface, permitting gas and nutrient exchange with the environment. A muscular layer just beneath the skin layer aids in locomotion. Flatworms are hermaphrodites and reproduce sexually. They typically have a life cycle involving a parasitic larval stage. Many types of flatworms are parasites of vertebrates. – Examples: Flatworms, flukes, tapeworms

Mesozoa -> Minute parasitic animals of invertebrates, particularly squids and octopuses. These worms have a simple, elongated, ciliated body. They reproduce sexually and have a complex life cycle involving more than one larval form. – Exmaple: Rhopalura granosa

Nemertea or Rhynchocoela -> Animals characterized by a proboscis, a long, muscular tube used in capturing invertebrate food. Nemerteans have elongated, flattened bodies and they lack an internal body cavity. They have a mouth opening for food ingestion and an anal opening for wastes. The blood of some nermerteans contains oxygen-carrying hemoglobin. Nemerteans reproduce sexually. – Examples: Nemertine worms, ribbon worms

Gastrotricha -> Microscopic multicellular animals that inhabit both freshwater and marine water. An external layer, the cuticle, encasing these animals contains cilia that aid in locomotion. Adhesive tubes found on the sides or at the posterior end aid in surface attachment. Freshwater species have a forked tail. These animals feed on dead or living bacteria, diatoms, or small protozoa. Marine species are hermaphroditic, while most fresh water species are female, reproducing by parthenogenesis. – Examples: Turbanella cornuta, Chaetonotus anomalus

Rotifera or Rotatoria -> Microscopic aquatic animals characterized by a corona, a wheel-shaped organ on the head used in feeding and swimming. The rapid beating of the cilia on the corona draws nutrient-containing water into the mouth. A protective cuticle covers the elongated, cylindrical body. Reproduction is sexual during brief periods of the year and throughout the rest of the year females reproduce via parthenogenesis. – Examples: Synchaeta oblonga, Phylodina roseola

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Herding Dog

Herding Dog

A herding dog or pastoral breed is a dog that either has been trained in herding or that is a member of a breed developed for herding.

Dogs can herd other animals in a variety of ways.

Some breeds, such as the Australian Cattle Dog, typically nip at the animals' heels.

Others, notably the Border Collie, get in front of the animals and use what is called eye to stare down the animals; they are known as headers.

The Koolie has been observed to use both these methods and to jump on the backs of their charges. All herding behavior is modified predatory behavior.

Commonly herded animals include cattle, sheep, and reindeer, although it is not unusual for poultry to be handled by dogs..

For more information about the topic Herding dog, read the full article at Wikipedia.org.

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The Animal Kingdom

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Kingdom Animalia includes more than one million living species, grouped into more than 30 phyla. Vertebrates, members of the phylum Chordata, comprise only one percent of these organisms. Phylum Arthropoda is more successful in sheer numbers, total mass, and distribution than all other groups of animals combined. The remaining animal phyla are composed of mostly marine-dwelling organisms.

THE MAJOR PHYLA:

• Acanthocephala (Spiny-Headed Worm)
• Annelida (Annelids)
• Arthropoda (Arthropods)-> subphyla: Chelicerata, Crustacea, and Unirama
• Brachiopoda (Lampshell)
• Chaetognatha (Arrowworm)
• Chordata (Chordates)-> subphyla: Cephalochordata, Tunicata, Vertebrata (fishes, amphibians, reptiles, birds, and mammals)
• Cnidaria (Cnidarians)
• Ctenophora (Comb Jellies)
• Cycliophora (Symbion)
• Echinodermata (Echinoderms)-> Subphyla: Pelmatozoa, Eleutherozoa
• Echiura (Spoonworm)
• Ectoprocta (Moss Animals) or Bryozoa
• Entoprocta (Entoprocts)
• Gastrotricha (Gastrotrich)
  Gnathostomulida (Gnathostomulid)
• Hemichordata (Acorn Worm)
• Kinorhyncha or Echinodera
• Loricifera (Loriciferan)
• Mesozoa
• Mollusca (Mollusk)
• Nematomorpha (Horsehair Worm)
• Nemertea or Rhynchocoela
• Nematoda (Roundworm)
• Onychophora (Velvetworm)
• Pentastomida (Tongueworm)
• Phoronida (Phoronids)
• Platyhelminthes (Flatworm)
• Pogonophora (Pogonophore)
• Porifera (Sponge)
• Rotifera (Rotifer)
• Sipuncula (Peanut Worm)
• Tardigrada (Tardigrade)
• Vestimentifera

CLASSIFICATION OF ANIMALS:

• Vertebrates
• Invertebrates

Animal Husbandry

Animal Husbandry pertains to breeding, feeding, and management of animals, or livestock, for the production of food, fiber, work, and pleasure. Modern methods concentrate on one type of animal in large, efficient farming units that generate animal products at the highest rate of return for investment. Intensive husbandry conditions include large numbers of animals in small lots, enriched feed, growth stimulation by various means, and vaccination against disease. Most of the world’s domestic animals, however, are raised in small units under less efficient conditions and at lower rates of return.

Animals furnish more than one-fourth of the world’s total value of agricultural products. They supply a much higher proportion of human food in the developed countries than elsewhere. In the United States, animal products account for more than one-half of the total agricultural income.

Traditional husbandry practices are closely associated with the degree of control needed over the animals that are kept and with the uses to which they are put. Most domesticated animals have multiple uses; for example, animals kept primarily for work also supply milk, meat, and clothing materials. The animals and their uses, however, are closely associated with the culture and experience of the people who care for them. In some regions of the world, cattle are not considered for use in the production of food. Studies have shown that the work power, fertilizer, milk, and the fuel from dung that the cattle provide in these regions are more efficient animal products than meat. Analysis of other cultural practices has often revealed unexpected efficiency of use fitted to local circumstances.

related topics:
• Draft Animals
• Sheep and Goats
• Cattle
• Poultry

Tardigrada

Tardigrade

Tardigrade, any of a group of tiny arthropod-like animals characterized by four pairs of stubby legs ending in large claws, a stout body, rounded back, and lumbering gait. They are also known as “water bears.” Tardigrades live worldwide in moist land habitats, along rocky shorelines, and on the bottoms of streams, lakes, and oceans. Their most striking feature is their ability to temporarily enter a nearly lifeless state known as anabiosis, which helps them survive environmental extremes. About 400 species of tardigrades are known and they range in length from 0.1 to 0.5 mm (0.004 to 0.02 in).

Tardigrades are most commonly found in association with the water film on mosses, liverworts, and lichens. Their densities may reach 2 million individuals per sq m (185,874 per sq ft) of moss. Some live in hot springs and a few live in a symbiotic relationship with or on the bodies of other animals. Tardigrades use a pair of oral stylets, or needle-like mouthparts, to pierce the walls of plant cells and feed on the liquid inside. Most species are plant eaters, but some are predators, feeding on tiny invertebrates and bacteria, and a few are detritivores, feeding on dead tissue and debris.

Scientific classification: Tardigrades make up the phylum Tardigrada. It is not clear to what other animals tardigrades are most closely related, but they are most similar to arthropods (insects, crustaceans, etc.), annelids (segmented worms), and gastrotrichs.