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]