Two of the classes of organisms in this phylum are
Two of the classes of organisms in this phylum are free-living, and one is parasitic. They have organ systems, albeit simple ones, but they lack special respiratory and circulatory structures. Since they have no internal cavity between the gut and the body wall, they are called acoelomate. FTP, name this phylum consisting of the classes Turbellaria, Trematoda, and Cestoda, which contains the flatworms.
Two of the classes of organisms in this phylum are free-living, and one is parasitic.
{Platyhelminthes}