SPINY-HEADED WORM

also called Acanthocephalan, any animal of the invertebrate phylum Acanthocephala. A proboscis, or snout, which bears hooks, gives the group its name. There are about 600 recorded species, all of which are parasites in vertebrates (usually fish) as adults and in arthropods as juveniles. The adults are usually less than 1 cm (0.4 inch) in length, but some reach 50 cm (about 20 inches) or more. Spiny-headed worms are found throughout the world.