The Collaborative International Dictionary of English v.0.48:

Trematodea \Trem`a*to"de*a\, n. pl. [NL., from Gr. ? having
   holes, from ?, ?, a hole.] (Zool.)
   An extensive order of parasitic worms. They are found in the
   internal cavities of animals belonging to all classes. Many
   species are found, also, on the gills and skin of fishes. A
   few species are parasitic on man, and some, of which the
   fluke is the most important, are injurious parasites of
   domestic animals. The trematodes usually have a flattened
   body covered with a chitinous skin, and are furnished with
   two or more suckers for adhesion. Most of the species are
   hermaphrodite. Called also Trematoda, and Trematoidea.
   See Fluke, Tristoma, and Cercaria.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Trematoda
    n 1: parasitic flatworms (including flukes) [syn: Trematoda,
         class Trematoda]