Acanthocephala

The thorny-headed worms, a phylum (formerly considered a class) of obligatory parasites without an alimentary canal, characterized by an anterior introvertible spiny proboscis. They superficially resemble nematodes but are cestode like in other traits, and hence are grouped as a distinctive phylum of helminths. In the adult stage they are parasites of vertebrate animals, mostly fish and amphibians; the larval stage is passed in invertebrates, chiefly crustaceans and insects. [acantho- + G. kephale, head]

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Acan·tho·ceph·a·la ə-.kan(t)-thə-'sef-ə-lə n pl a group of elongated parasitic intestinal worms with a hooked proboscis that as adults lack a digestive tract and absorb food through the body wall, and that are usu. classified as a separate phylum related to the phylum Platyhelminthes

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Acan·tho·ceph·a·la (ə-kan″tho-sefґə-lə) [acantho- + Gr. kephalē head] the thorny-headed worms, a phylum of parasites often infesting animals, so called because of the proboscis projecting anteriorly that is covered with thornlike spines for attachment to the digestive tract of the host. In some systems of classification, they are considered to be a class of the phylum Nemathelminthes.