Polymorphida

{{Short description|Order of thorny-headed worms}}

{{Automatic taxobox

|taxon=Polymorphida

|authority=Petrochenko, 1956

| image = C wegeneri.JPG

| image_caption = Corynosoma wegeneri

}}

Polymorphida are an order of thorny-headed worms (phylum Acanthocephala). The adults of these parasitic platyzoans feed mainly on fish and aquatic birds.

This order contains 5 families:{{Cite web | url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=197470 | title=ITIS - Report: Polymorphida }}Huston, D. C., Cribb, T. H., & Smales, L. R. (2020). Molecular characterisation of acanthocephalans from Australian marine teleosts: proposal of a new family, synonymy of another and transfer of taxa between orders. Systematic Parasitology, 1-23.

• Centrorhynchidae Van Cleave, 1916
• Isthomosacanthidae Smales, 2012
• Plagiorhynchidae Meyer, 1931
• Pyriprobosicidae
• Polymorphidae Meyer, 1931