Source : Webster's Revised Unabridged Dictionary (1913)

Tristoma \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.