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:
^ "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.