The flatworms or Platyhelminthes are wormlike animals with a single major opening to the gut. This opening functions as both a mouth and an anus. Between the gastrodermis (lining of the gut) and the epidermis, the body is filled with tissues, including layers of muscle, connective tissue, and reproductive organs. Included in the flatworms are free-living forms (class Turbellaria), and two major groups of animal parasites (class Trematoda-flukes-and class Cestoda- tapeworms). Most tubellarians are bottom dwellers in marine water or freshwater or live in moist terrestrial environments, but a few species are symbiotic or parasitic. The majority of the larger species are found on the underside of rocks or other hard objects in freshwater streams or in the littoral zones of the ocean. All of the cestodes and trematodes exist as endoparasites and most exhibit indirect life cycles with more than one host. The initial host is usually an invertebrate, and the final host is most often a vertebrate. Anumber of species utilize humans as a final host.
Thanks for description - Animal life club