The mouth is located somewhere on the ventral midline and opens into a blind gut, or gastrovascular cavity, which lacks an anus and sometimes lacks a lumen. The body is cylindrical in small species (that may be as small as ciliated protozoa) and dorsoventrally flattened in larger species. Neoophorans includes 4500 described species of free-living flatworms. Flatworms have elaborate hermaphroditic reproductive systems. As in other bilateral animals, there is an anterior brain and associated sense organs. The gut, if present, has a single opening to the exterior. Unlike most triploblastic animals, they have no body cavity and no blood system. Modified, with permission, from Invertebrate Anatomy OnLineĬopyright 2003 by Richard Fox (Lander University)įlatworms, or platyhelminths, are bilaterally symmetrical and have three tissue layers.
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