The Collaborative International Dictionary of English v.0.48:

Oligochaeta \Ol`i*go*chae"ta\, Oligochaeta \Ol`i*go*chae"ta\,
   prop. n. pl. [NL., fr. Gr. 'oli`gos little, pl., few + ?
   hair.] (Zool.)
   An order of Annelida which includes the earthworms and
   related species, including some small freshwater species.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Annelida \An*nel"i*da\, n. pl. [NL. See Annelid.] (Zool.)
   A division of the Articulata, having the body formed of
   numerous rings or annular segments, and without jointed legs.
   The principal subdivisions are the Ch[ae]topoda, including
   the Oligoch[ae]ta or earthworms and Polych[ae]ta or
   marine worms; and the Hirudinea or leeches. See
   Ch[ae]topoda.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Oligochaeta
    n 1: earthworms [syn: Oligochaeta, class Oligochaeta]