Acanthocephala are one of the least speciose taxa of parasitic helminth, with the number of described species at about 1000. Life cycles are consistent, with the same progression of life cycle stages, but of course there are differences in the host species involved. Adult morphology, both males and females, is important for identification. Key features are the number, shape and arrangement of hooks on the proboscis; structure of nuclei in the body wall, cement gland arrangement in males, and ligament sac structure in females.