An order of the Acanthocephala, the adults of which are parasitic worms found in fishes, aquatic birds, and mammals. They have the following characteristics. The nuclei of the hypodermis are fragmented and the chief lacunar vessels are lateral. The males have usually two to seven cement glands. The ligament sac in the female breaks down so that the eggs develop in the body cavity. Proboscis hooks occur in long rows and spines are present on the body of some species. Species which commonly occur in vertebrates are Leptorhynchoides thecatus and Corynosoma.