Phylum Acanthocephala is a group of parasitic worms that lack a digestive system and live inside their hosts. Some synonyms for this phylum include thorny-headed worms, spiny-headed worms, and spiny-headed parasites. These worms are characterized by a retractable proboscis that is covered in spines. They use the proboscis to attach to the host's intestinal wall and feed on their blood and tissue. The Acanthocephala phylum has a worldwide distribution and can infect a variety of hosts, including fish, birds, mammals, and even humans. It is important to understand the characteristics of these worms in order to prevent and treat infections in both animals and humans.