- 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.
* * *Platy·hel·min·thes .plat-i-hel-'min(t)-thēz n pl a phylum of soft-bodied bilaterally symmetrical usu. much flattened invertebrates comprising the planarians, flukes, tapeworms, and related worms, having the body unsegmented or composed of a series of proglottids formed by strobilation, built up of ectoderm, endoderm, and mesoderm, and without body cavity, the space between the body wall and the various organs being filled with parenchyma, and distinguished by an excretory system made up of tubules that permeate the body and usu. communicate with the exterior and that end internally in flame cells
* * *Platy·hel·min·thes (plat″ĭ-həl-minґthēz) [platy- + Gr. helmins worm] the flatworms, a phylum of acoelomate, dorsoventrally flattened, bilaterally symmetrical invertebrates; classes include Turbellaria, Trematoda, and Cestoidea.
Medical dictionary. 2011.