Animal Classification
Rotifera(Rotifers or "wheel animals")
Rotifers live in lakes, rivers, streams, and the oceans. They have cylinder- or vase- shaped bodies. On their heads are circles of hairlike projections known as cilia. The largest rotifers are about 1/10 inch (3 millimeters) long. About 2,000 species have been identified.
Bryozoa (Bryozoans)
Bryozoans live in water, and most form colonies. Some colonies are jellylike masses. Others form branchlike networks on water plants. Bryozoans have a boxlike or tube-shaped body that holds fluid. Tentacles (feelers) cluster on the head. About 5,000 species have been identified.
Cnidaria (Cnidarians or coelenterates)
Cnidarians may be shaped like a cylinder, a bell, or an umbrella. Their bodies contain a jellylike material between two layers of cells. This phylum includes jellyfish, sea fans, sea anemones, and corals. About 9,000 species have been identified.
Brachiopoda (Lamp shells)
Lamp shells have two hard shells that cover a soft body. They live in the oceans. Some attach themselves to rocks and other hard surfaces. Others burrow or lie loose in sand or mud. About 335 living species have been identified, and about 30,000 extinct species have been described.
Acanthocephala (Spiny-headed worms)
These parasites live in many animals. They have a spiny tubelike structure called a proboscis on their head that attaches them to the wall of their hosts' intestines. Most measure about 3/4 inch (2 centimeters) or less in length. About 600 species have been identified.
Porifera (Sponges)
Sponges attach themselves to rocks and other objects at the bottom of oceans, lakes, or rivers. Many take the shape of such objects. Sponges have cells called choanocytes or collar cells that trap food particles within chambers in their bodies. About 5,000 species of sponges have been identified.
Ctenophora (Comb jellies or sea walnuts)
These transparent animals live in oceans. They have eight bands of comblike organs on the side of their bodies. Most are pea-sized to thimble-sized. Comb jellies of a group called Venus' girdle can be over 3 feet (90 centimeters) long. About 90 species have been identified.
Nematoda (Roundworms or nematodes)
Many roundworms live in soil, water, or dead tissue. Some are parasites that are found in living plants and animals. Roundworms range from microscopic to about 3 feet (90 centimeters) long. The phylum includes filariae, hookworms, pinworms, and trichinae. About 12,000 species have been identified.
Platyhelminthes (Flatworms)
Many flatworms live as parasites in other animals. Flatworms have soft, thin, flattened bodies with three layers of cells. Most are less than 1 inch (2.5 centimeters) long. The largest flatworms, called tapeworms, are as long as 100 feet (30 meters). About 13,000 species have been identified.
Nemertea or Rhynchocoela (Ribbon worms or proboscis worms)
Most ribbon worms live in the oceans. They have a slender, often flattened, body. They shoot out a proboscis from their head to capture prey. Most of these worms range from less than 1 inch (2.5 centimeters) to 8 inches (20 centimeters) long, but one species can reach a length of 100 feet (30 meters). About 900 species of ribbon worms have been identified.
Annelida (Segmented worms)
The bodies of these worms consist of segments. Many of these worms have tentacles on their heads and a pair of leglike projections called parapodia on each body segment. Earthworms and leeches belong to this phylum. About 8,800 species have been identified.
Chaetognatha (Arrow worms)
These worms have an arrow shape. They range from about 1/4 to 6 inches (0.5 to 15 centimeters) long. They have movable hooks on their heads that they use to catch prey. They live in open seas, particularly in warm waters. About 100 species have been identified.
Arthropoda (Arthropods)
Arthropods have jointed legs, segmented bodies, and an outside shell called an exoskeleton. This phylum includes insects, such as ants, bees, beetles, and butterflies; crustaceans, such as crabs, lobsters, and shrimps; arachnids, such as mites, ticks, and spiders; centipedes; and millipedes. More than 1 million species have been identified.
Echinodermata (Echinoderms)
Echinoderms are spiny-skinned animals that have an internal bony skeleton. They are the only animals that have tiny tubelike structures called tube feet. This phylum includes brittle stars, sand dollars, sea urchins, sea cucumbers, and starfish. About 6,000 species have been identified.
Mollusca (Mollusks)
Mollusks make up the largest group of water animals, though some species live on land. Most mollusks have a hard shell that protects a soft body. The phylum includes clams, mussels, octopuses, oysters, snails, and squids. About 50,000 living species have been identified, and fossils of 100,000 extinct species have been found.
Chordata (Chordates)
At some point in their life cycle, all chordates have a notochord (a rodlike, flexible cord
that runs down the back of the body). A hollow nerve tube runs above the notochord. This phylum is the one to which human beings and many familiar animals belong. It includes amphibians, birds, mammals, and reptiles, as well as hagfishes, lampreys, and bony fishes.
About 45,000 species have been identified.
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