Oligochaeta n. pl. : An order of Annelida which includes the earthworms and related species.

Example:
what the differences between Polychaeta, Oligochaeta, and Hirudenia?

Taxonomy
Oligochaeta, Michaelsen, Earthworm, worms, species, Vejdovsky, segment, body, aquatic oligochaetes, vessels, Erséus, Claus, Bouché, free encyclopedia, aquatic, food, Brinkhurst, Jamieson.

Defination from the web:
Oligochaeta (singular Oligochaete, pronounced /ˈɒlɨɡɵkiːt/) is a subclass in the biological phylum Annelida and includes various earthworms. ... Phylogeny of the Megascolecidae and Crassiclitellata (Annelida, Oligochaeta): combined versus partitioned analysis using nuclear (28S) and ...