Polycladida

flatworm order

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June 18, 2026

Quick Summary

The Polycladida are an order of marine flatworms. These are broad, flattened, and often brightly colored creatures. A key characteristic of their alimentary tract is that it has many primary branches radiating from a central cavity. They also possess numerous ovaries and testes, but no vitellarium. The term "polyclad" itself refers to a flatworm belonging to this order. While many flatworms are hermaphroditic, with complex reproductive systems, the Polycladida are distinguished by having numerous ovaries and testes and lacking a vitellarium.123

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flatworm
Annotated classification
Order Polycladida Pharynx simple, bulbose, or plicate (many ridges); intestine may have short diverticula, or pockets; protonephridia paired; testes usually numerous; penis papilla generally present; nervous system with 3–4 trunks; nearly 800 species. Class Monogenea Oral sucker lacking or weakly developed; posterior end with
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Order Polycladida Pharynx simple, bulbose, or plicate (many ridges); intestine may have short diverticula, or pockets; protonephridia paired; testes usually numerous; penis papilla generally present; nervous system with 3–4 trunks; nearly 800 species. Class Monogenea Oral sucker lacking or weakly developed; posterior end with
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