Platyhelminthes

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Platyhelminthes A phylum of acoelomate invertebrates comprising the flatworms, characterized by a flattened unsegmented body. The simple nervous system shows some concentration of cells at the head end. The mouth leads to a simple branched gut without an anus. Flatworms are hermaphrodite but self-fertilization is unusual. Many species are parasitic. The phylum contains the classes Turbellaria (planarians), Trematoda (flukes), and Cestoda (tapeworms).

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