noun.
Any of various annelid worms of the class (or subclass) Oligochaeta, including the earthworms and aquatic species found chiefly in freshwater, which lack the appendages typical of polychaetes.
The Century Dictionary and Cyclopedia
Belonging to or having the characteristics of the Oligochæta.
noun.
A worm of the order Oligochæta.
the GNU version of the Collaborative International Dictionary of English
noun.
Any of an order of hermaphroditic terrestrial and aquatic annelids (including the earthworms) having bristles borne singly along the length of the body; a member of the Oligochaeta.