flatworm Simple, carnivorous, ribbon-like creature which, having no circulatory system and sometimes no mouth or gut, feeds by absorption through its body wall. The fluke and tapeworm are both animal parasites. Order Platyhelminthes.

flat·worm / ˈflatˌwərm/ • n. a worm of a phylum (Platyhelminthes) that includes the planarians together with the parasitic flukes and tapeworms. They are distinguished by having a simple flattened body that lacks blood vessels, and a digestive tract that, if present, has a single opening.

flatworm (platyhelminth) (flat-werm) n. any of the flat-bodied worms, including the flukes and tapeworms. Both these groups contain many parasites of medical importance.