The Collaborative International Dictionary of English v.0.48:

Platyelminthes \Plat`y*el*min"thes\, n. pl. [NL. See Platy-,
   and Helminthes.] (Zool.)
   A class of helminthes including the cestodes, or tapeworms,
   the trematodes, and the turbellarians. Called also
   flatworms.
   [1913 Webster]