Topic: Platyhelminthes

Platyhelminthes , phylum containing about 20,000 species of soft-bodied, bilaterally symmetrical, invertebrate animals, commonly called flatworms. There are four classes: the free-living, primarily aquatic class, Turbellaria, and Trematoda, Cestoda, and Monogenea, which are considerably modified for their exclusively parasitic existence. While the structure of the flatworms marks a major step in animal evolution, their origin and relationships within the group are still controversial. Anatomy Flatworms are dorso-ventrally flattened. The epidermis is generally ciliated in the turbellarians,... Read more