Palaeacanthocephala

Palaeacanthocephala ("ancient thornheads") is a class within the phylum Acanthocephala. The adults of these parasitic platyzoans feed mainly on fish, aquatic birds and mammals. This order is characterized by the presence of lateral longitudinal lacunar canals and a double-walled proboscis receptacle.^[1] The nuclei of the hypodermis (outer layer of skin) are fragmented and the males have two to seven cement glands, unlike their relatives the Archiacanthocephala, which always have eight.

Palaeacanthocephala
Proboscis of a Rhadinorhynchus species
Scientific classification
Kingdom:	Animalia
Phylum:	Acanthocephala
Class:	Palaeacanthocephala Meyer, 1931
Orders
Echinorhynchida Heteramorphida Polymorphida

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

There are three orders in the class Palaeacanthocephala:^[2]

• Echinorhynchida Southwell and Macfie, 1925
• Heteramorphida Amin and Ha, 2008
• Polymorphida Petrochenko, 1956