Acanthocephala

Acanthocephala (Greek , '''' 'thorn' + , '''' 'head') is a group of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an eversible proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans have complex life cycles, involving at least two hosts, which may include invertebrates, fish, amphibians, birds, and mammals. About 1,420 species have been described.

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

Archiacanthocephala is a class within the phylum of Acanthocephala. They are parasitic worms, which attach themselves to the intestinal wall of terrestrial vertebrates, including humans. They are characterised by the body wall and the lemnisci (which are a bundle of sensory nerve fibers), which have nuclei that divide without spindle formation, or the appearance of chromosomes, or it has a few amoebae-like giant nuclei. Typically, there are eight separate cement glands in the male, which is one of the few ways to distinguish the dorsal and ventral sides of these organisms.

Eoacanthocephala is a class of parasitic worms, within the phylum Acanthocephala. They feed on any aquatic cold-blooded creature such as turtles and fish. Their proboscis spines are arranged radially, with no protonephridia, and with persistent ligament sacs in female. The only reliable way to identify the group is that they only have one cement gland. This is a primitive characteristic and hence the name. The class contains 2 orders:

Rhadinorhynchus is a genus of worms belonging to the family Rhadinorhynchidae.

Polyacanthorhynchidae is a family of parasitic worms from the phylum Acanthocephala. It contains a single genus Polyacanthorhynchus.