OLIGOCHAETE

any worm of the class Oligochaeta (phylum Annelida). About 3,200 living species are known, the most familiar of which is the earthworm (q.v.), Lumbricus terrestris. Oligochaetes are common all over the world. They live in the sea, in fresh water, and in moist soil. Oligochaetes, which range in length from a few millimetres (a fraction of an inch) to more than 3 m (10 feet), are notable for the absence of a head and parapodia, the flat, lobelike outgrowths used by many other annelids for locomotion. They have few setae, or bristles, on the body. Many species have a clitellum, a thickened region that secretes cocoons for enclosing eggs. All forms are hermaphroditic; i.e., the functional reproductive organs of both sexes occur in the same individual. Development and growth are direct, with no larval stages. Oligochaetes, in particular the earthworm, are ecologically important in their roles of turning over and aerating the soil; the earthworm is secondarily important as fish bait.