Palaeacanthocephala

thumb|Two paleoacanthocephalans, Heterosentis mongcai Amin, Heckmann & Ha, 2014 and Filisoma indicum Van Cleave, 1928

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

Echinorhynchida, from Ancient Greek ἐχῖνος (ekhînos), meaning "hedgehog", and ῥύγχος (rhúnkhos), meaning "snout", is an order of parasitic worms in the phylum Acanthocephala. It contains 13 known families: Arhythmacanthidae Yamaguti, 1935 Cavisomidae Meyer, 1932 Diplosentidae Tubangui and Masiluñgan, 1937 Echinorhynchidae Cobbold, 1876 Fessisentidae Van Cleave, 1931 Gymnorhadinorhynchidae Braicovich, Lanfranchi, Farber, Marvaldi, Luque and Timi, 2014 Heteracanthocephalidae Petrochenko, 1956 Illiosentidae Golvan, 1960 Isthmosacanthidae Smales, 2012 Pomphorhynchidae Yamaguti, 1939 Rhadinorhynch

Golvanacanthus is a monotypic genus of acanthocephalans (thorny-headed or spiny-headed parasitic worms) containing a single species, Golvanacanthus blennii, that infests animals.