Tristoma

Tris´to`ma

    (trĭs´tô`må)
n.1.(Zool.) 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.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.