Earthworms are classified as Annelida.
Annelida mean little rings whichrefers to the many segments in their body. The structure of an earthwormsbody is made up of more than one hundred segments separated by partitions thatdivide the coelum. All segments are identical except by the anterior andposterior ends.
The anterior segments reflect the cephalization that is anadaption of burrowing. The head of the earthworm contains the sense organs. Themuscle lines that make up the interior body wall are circular and longitudinal.Earthworms move by anchoring some segments by their setae and contracts thecircular muscles in front of those segments, producing fluid pressure in theanterior coelom cavities.
The anterior setae grip the ground, the longitudinalmuscles contract pulling the posterior along. Earthworms burrow and feed on soiland organic matter at the same time. They digest the organic matter andeliminate wastes and undigested matter as dirt and feces called castings.
Earthworms are good for the soil because they sucked up soil into the by themuscular pharynx. The soil then passes through a tubelike esophagus to atemporary storage called a crop, and from there to the gizzard. The gizzardwalls grind the soil, releasing and breaking up organic matter. Through theearthworms body via a closed circulatory system it transports oxygen,nutrients, and wastes.
The blood travels from the anterior to the posteriorthrough ventral blood vessel and then forward through a dorsal vessel. Aorticarches are five tubes that link the major vessel near the anterior. Smallervessels branch into each segment of the body. Earthworms have no respiratorysystem or no gills. Carbon dioxide and oxygen diffuse directly across the skin.This process can only happen if the skin is moist.
Earthworms secretions ofmucus and a thin cuticle help keep the skin moist. Through a long tube callednephridia the earthworms eliminate nitrogenous wastes. Earthworms are sensitiveto touch, light, vibrations, moisture, chemicals, and temperatures. Other senseorgans and the nerves that control individual muscle contractions are present ineach segment. Earthworms are hermaphrodites, but one worm cannot fertilize itown 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 themucus.
One of their sperms goes to a pouchlike seminal receptable. After aseveral days a mucus and chitin sheath is secreted by the clitelllum a swellingaround the sex organs. When the worm wriggles to slip the sheath off its body,eggs, and sperm are joined and fertilization occurs.Zoology and Animals