\Tris"to*ma\, n. [NL., from Gr. ? (see {Tri-}) + ?
mouth.] (Zo["o]l.)
Any one of numerous species of trematode worms belonging to
{Tristoma} and allied genera having a large posterior sucker
and two small anterior ones. They usually have broad, thin,
and disklike bodies, and are parasite on the gills and skin
of fishes.