Earthworms are classified as Annelida. Annelida mean little rings which refers to the many segments in their body. The structure of an earthworms body is made up of more than one hundred segments separated by partitions that divide the coelum. All segments are identical except by the anterior and posterior ends. The anterior segments reflect the cephalization that is an adaption of burrowing. The head of the earthworm contains the sense organs. The muscle lines that make up the interior body wall are circular and longitudinal. Earthworms move by anchoring some segments by their setae and contracts the circular muscles in front of those segments, producing fluid pressure in the anterior coelom cavities. The anterior setae grip the ground, the longitudinal muscles contract pulling the posterior along. Earthworms burrow and feed on soil and organic matter at the same time. They digest the organic matter and eliminate wastes and undigested matter as dirt and feces called castings. Earthworms are good for the soil because they sucked up soil into the by the muscular pharynx.
The soil then passes through a tubelike esophagus to a temporary storage called a crop, and from there to the gizzard. The gizzard walls
Through a long tube called nephridia the earthworms eliminate nitrogenous wastes. Earthworms are sensitive to touch, light, vibrations, moisture, chemicals, and temperatures. Other sense organs and the nerves that control individual muscle contractions are present in each segment. Earthworms are hermaphrodites, but one worm cannot fertilize it own eggs. When earthworms are join to head to tail its called mating. Together they form a mucus around each other. They both inject sperm into the mucus. One of their sperms goes to a pouchlike seminal receptable. After a several days a mucus and chitin sheath is secreted by the clitelllum a swelling around the sex organs. When the worm wriggles to slip the sheath off its body, eggs, and sperm are joined and fertilization occurs.