trematode /trem″ətōd/ [Gk, trematodes, pierced] , any species of flatworm of the class Trematoda, some of which are parasitic to humans, infecting the liver, the lungs, and the intestines. Kinds of trematodes include the organisms causing clonorchiasis, fascioliasis, paragonimiasis, schistosomiasis. See also fluke.