The Collaborative International Dictionary of English v.0.48:

Etheostomoid \E`the*os"to*moid\, a. [NL. etheostoma name of a
   genus + -oid.] (Zo["o]l.)
   Pertaining to, or like, the genus Etheostoma. -- n. Any
   fish of the genus Etheostoma and related genera, allied to
   the perches; -- also called darter. The etheostomoids are
   small and often bright-colored fishes inhabiting the fresh
   waters of North America. About seventy species are known,
   including the rare snail darter (Percina tanasi), 3
   inches long, found only in the Tennessee River and classified
   as a threatened species. See Darter.
   [1913 Webster]

WordNet (r) 3.0 (2006):

snail darter
    n 1: a small snail-eating perch of the Tennessee River [syn:
         snail darter, Percina tanasi]