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Palpigradi

A palpigrade, commonly known as a microwhip scorpion, is an invertebrate animal belonging to the order Palpigradi in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda.

Contents

Physical description

Palpigrades are tiny cousins of the uropygids, or whip scorpions, no more than 3 millimetres (0.12 in) in length. They have a thin, pale, segmented integument, and a segmented abdomen that terminates in a whip-like flagellum, made up of 15 segment-like parts, or "articles". The carapace is divided into two plates between the third and fourth leg pair of legs. They have no eyes.

As in some other arachnids, the first pair of legs are modified to serve as sensory organs, and are held clear of the ground while walking. Unusually, however, palpigrades use their pedipalps for locomotion, so that the animal appears to be walking on four pairs of legs.

Some palpigrades have three pairs of abdominal lung-sacs, although these are not true book lungs as there is no trace of the characteristic leaflike lamellae which defines book lungs. However, many species have no respiratory organs at all and breath directly through the cuticle.[1]

Behavior

As of 2003, very little is known about palpigrade behavior. They are believed to be predators like their larger relatives, feeding on minuscule insects in their habitat. Their mating habits are unknown, except that they lay only a few relatively large eggs at a time.

Habitat

Microwhip scorpions need a damp environment to survive, and they always hide from light, so they are commonly found in the moist earth under buried stones and rocks. They can be found on every continent, except in Arctic and Antarctic regions.

As of 2000, approximately 80 species of palpigrades have been described worldwide, all in the family Eukoeneniidae, which contains 4 genera.

Fossil record

A single fossil palpigrade species has been described from the ?Pliocene Onyx Marble of Arizona, USA[2]. Its familial position is uncertain. Older publications refer to a fossil palpigrade (or palpigrade-like animal) from the Jurassic of the Solnhofen limestone in Germany [3], but this has now been shown to be a misidentified fossil insect [4].

See also

References

  1. ^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadephia, PA: Holt-Saunders International. p. 614. ISBN 0-03-056747-5. 
  2. ^ Rowland, J. M. & Sissom, W. D. 1980. Report on a fossil palpigrade from the Tertiary of Arizona, and a review of the morphology and systematics of the order (Arachnida: Palpigradida). Journal of Arachnology, 8: 69–86
  3. ^ Haase, E. 1890. Beitrag zur Kenntniss der fossilen Arachniden. Zeitschrift der Deutsche geologische Gesellschaft, 1890: 629–657.
  4. ^ Delclòs, X., Nel, A., Azar, D., Bechly, G., Dunlop, J. A., Engel, M. S., Heads, S. W. 2008. The enigmatic Mesozoic insect taxon Chresmodidae (Polyneoptera): New palaeobiological and phylogenetic data, with the description of a new species from the Lower Cretaceous of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 247: 353–381
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