Pentastomida

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iTongue worms

Linguatula taenioides, a pentastomid parasite of sheep

Scientific classification

Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Maxillopoda
Subclass:	Pentastomida Diesing, 1836

Orders

Cephalobaenida
Porocephalida

The Pentastomida are a group of parasitic invertebrates commonly known as tongue worms due to the resemblance of some species to a vertebrate tongue.

There are about 100 extant species of pentastomids; all are obligate parasites with correspondingly degenerate anatomy. Adult tongue worms vary from about 1 cm to 14 cm in length, and parasitize the respiratory tracts of vertebrates <ref>Cooper Curtice (1890). The animal parasites of sheep. Washington: Government Printing Office.</ref>. They have five anterior appendages. One is the mouth; the others are two pairs of hooks which they use to attach to the host. This arrangement led to their scientific name, meaning "five openings", but although the appendages are similar in some species, only one is a mouth.

Their affinity with other invertebrates is uncertain. They grow by moulting, which suggests they belong to the Ecdysozoa. Historically, they were considered to deserve a phylum of their own, but in 1972, Wingstrand showed similarities in the structure of spermatozoa between pentastomids and branchiurans (fish lice), a group of parasitic crustaceans <ref>K. G. Wingstrand (1972). Comparative spermatology of a pentastomid, Raillietiella hemidactyli, and a branchiuran crustacean, Argulus foliaceus, with a discussion of pentastomid relationships. Kong. Danske Videnskabelige Selsk. Biol. Skrift. 19: 1–72.</ref>, and this relationship is supported by molecular evidence <ref>L. Abele, W. Kim, and B. E. Felgenhauer (1989). Molecular evidence for inclusion of the phylum Pentastomida in the Crustacea. Mol. Biol. Evol. 6: 685–691.</ref>.

However, fossils from the Upper Cambrian identified as pentastomids (Heymonsicambria, Haffnericambria, Bockelericambria) suggest that the pentastomids branched very early and may be an outgroup to the other arthropods <ref>D. Walossek and K. J. Müller (1998). “Cambrian "Orsten"-type arthropods and the phylogeny of Crustacea”, R. A. Fortey and R. H. Thomas: Arthropod Relationships. London: Chapman & Hall, 139–143.</ref>.

Alternative names for the Pentastomida include Pentastoma (strictly a genus name), Linguatulida, and Acanthotheca.

[edit] Classification

This article follows Martin and Davis in placing Pentastomida in the class Maxillopoda within the subphylum Crustacea <ref>Joel W. Martin and George E. Davis (2001). An Updated Classification of the Recent Crustacea. Natural History Museum of Los Angeles County.</ref>. Martin and Davis present this classification of the pentastomids down to the level of families:

Subclass Pentastomida Diesing, 1836