Earthworm structure

How is the anatomy and physiology of an Earthworm classified?
Earthworms are hermaphrodite and have both male and female reproductive cells. They cannot self-fertilise, however, and must find a mate to exchange sperm cells with. Earthworms reach sexual maturity at about four weeks old. This species comes to the surface to mate. Copulation, which may take up to an hour, involves two worms lying together with their heads pointing in opposite directions. While mating, the worms seem to shut out all other external stimuli and do not respond to light or touch. Large amounts of mucus are released by both individuals and while closely pressed against one another, sperm is exchanged. After this is complete the worms separate. After mating the clitellum begins to secrete a substance which hardens to form a ri...