1. A phylum of flatworms that are bilaterally symmetric, flattened, and acelomate. There is no digestive tract in some platyhelminths (Cestoda), or the gut may be incomplete (without an anus), as in the Trematoda; most of the forms are hermaphroditic. There are three major classes, but the parasitic species of medical and veterinary importance are in the subclass Cestoda (the true tapeworms) of the class Cestoidea, and in the subclass Digenea (the digenetic flukes) of the class Trematoda.
The definition information for Platyhelminthes is provided by Stedman's. You can search our medical dictionary here.