- any of various annelids of the family Oligochaeta, including earthworms and certain small, freshwater species, having locomotory setae sunk directly in the body wall.
- any freshwater or terrestrial annelid worm of the class Oligochaeta, having bristles (chaetae) borne singly along the length of the body: includes the earthworms
- of, relating to, or belonging to the class Oligochaeta
- Any of various annelid worms of the class Oligochaeta. Oligochaetes, unlike polychaetes, have relatively few bristles (called setae) along the body, and often have a thickened, ringlike region (called a clitellum) that secretes a substance used for enclosing eggs in a cocoon. Oligochaetes include the earthworms and a few small freshwater forms. Compare polychaete.