Adults live as endoparasites in the alimentary canal of all classes of vertebrates in marine, freshwater, and terrestrial habitats and larvae live in the body cavity of arthropods. The arthropod becomes infected by eating the mature egg, from which the acanthor larva is freed into the lumen of the invertebrate's digestive tract. Later, this larva bores into the gut wall and enters the hemocoel. Here, development of the parasite proceeds through the acanthella stage up to the cystacanth stage, which can infect the vertebrate host after the arthropod is ingested. Acanthocephala exhibit considerable uniformity of structure and similarity in life cycles and reproductive processes.
All acanthocephalan worms are dioecious and their reproductive organs are highly characteristic.
Acanthocephala have cylindrical or flattened bodies, usually white in color, with some species slightly yellow to orange. Most species are not much more than 1 cm in length, but some measure up to 70 cm. According to this scheme the phylum consisting of four classes, namely Palaeacanthocephala, Archiacanthocephala, Polyacanthocephala and Eoacanthocephala. In this phylum sexual reproduction is the only form that occurs. More work has been done on spermatogenesis and the structure of the spermatozoa than on the testes.