Platyhelminthes

CE5

A. Planaria, representative of the phylum Platyhelminthes B. Internal anatomy of Planaria

Platyhelminthes plătˌēhĕlmĭnˈthēz [key], 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.

Sections in this article:

• Introduction
• Class Monogenea
• Class Cestoda
• Class Trematoda
• Class Turbellaria
• Anatomy

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