Article
Article
Platyhelminthes
Article By:
Rohde, Klaus Department of Zoology, University of New England, Armidale, New South Wales, Australia.
Goodchild, C. G. Emory University, Atlanta, Georgia.
Last reviewed:January 2021
DOI:https://doi.org/10.1036/1097-8542.527600
A phylum of the invertebrates, commonly called the flatworms. They are bilaterally symmetrical, nonsegmented worms characterized by lack of coelom, anus, circulatory and respiratory systems, and exo- and endoskeletons. Many species are dorsoventrally flattened. They possess a protonephridial (osmoregulatory-excretory) system, a complicated hermaphroditic reproductive system, and a solid mesenchyme which fills the interior of the body. Some parasitic species, that is, some trematodes, have secondarily acquired a lymphatic system resembling a true circulatory system. Some species of trematodes, the schistosomes, have separate sexes.
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