Acanthocephala (
Greek , , thorn + , , head) is a
phylum 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, fishes,
amphibians, birds, and
mammals. About 1150
species have been described.