Acanthocephalans

Acanthocephala (Greek ἄκανθος, akanthos, thorn + κεφαλή, kephale, head) is a phylum of parasitic worms known as acanthocephalans, thorny-headed worms, or spiny-headed worms, characterized by the presence of an evertable 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, fishes, amphibians, birds, and mammals. About 1150 species have been described.

The Acanthocephala were thought to be a discrete phylum. Recent genome analysis has shown that they are descended from, and should be considered as, highly modified rotifers. This is an example of molecular phylogenetics. This unified taxon is known as Syndermata.