The Acanthocephala (gr. Acanthus — thorn Kephale — head) is a phylum of parasitic worms, characterised by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans typically have complex life cycles, involving a number of hosts, including invertebrates, fishes, amphibians, birds, and mammals.