Source : Webster's Revised Unabridged Dictionary (1913)

Oligochaeta \Ol`i*go*ch[ae]"ta\, n. pl. [NL., fr. Gr. ? little,
   pl., few + ? hair.] (Zo["o]l.)
   An order of Annelida which includes the earthworms and
   related species.

Annelida \An*nel"i*da\, n. pl. [NL. See {Annelid}.] (Zo["o]l.)
   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}.

Source : WordNet®

Oligochaeta
     n : earthworms [syn: {class Oligochaeta}]