Schizomida

Schizomida
	Female Hubbardia pentapeltis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Order:	Schizomida; Petrunkevitch, 1945
Families
	† Calcitronidae Petrunkevitch, 1945b; Hubbardiidae Cook, 1899; Protoschizomidae Rowland, 1975

Schizomida (common name shorttailed whipscorpion)^[1] is an order of arachnids, superficially resembling spiders and generally less than 5 millimetres (0.20 in) in length.

The order is not yet widely studied. As of 2005, more than 230 species of schizomids have been described worldwide, most belonging to the Hubbardiidae family. A systematic review including a full catalogue may be found in Reddell & Cokendolpher (1995).

Anatomy

File:Schizomus tenuicaudatus.jpg

Female Schizomus tenuicaudatus

Schizomids are relatively small, soft-bodied arachnids, somewhat similar in appearance to whip scorpions. The prosoma (cephalothorax) is divided into three regions, each covered by plates, the large protopeltidium and the smaller, paired, mesopeltidia and metapeltidia. The name means "split or cleaved middle", referring to the way the thorax is divided into two separate plates.^[2]

The opisthosoma (abdomen) is a smooth oval of 12 recognizable segments. The first is reduced and forms the pedicel, while the last three are constricted, forming the pygidium. The last segment bears a short whip-like tail or flagellum, consisting of no more than four segments.

Like the related orders Thelyphonida, Amblypygi, and Solifugae, the schizomids use only six legs for walking, having modified their first two legs to serve as sensory organs. They also have large well-developed pincer-like pedipalps just before the sensory legs. The hind legs are modified for jumping, as part of their escape response when threatened^[3]. Schizomids have no actual eyes, but a few species have vestigial eyespots capable of telling light from dark.

Habitat

Schizomids are generally tropical creatures, although some populations have been found in California and Arizona. They tend to live in the top layer of soil and in the cavities beneath logs and rocks, where they can avoid desiccation. They seek water and avoid light. Some species are cave dwellers, and a few live in or near termite or ant colonies.

Subtaxa

Schizomids are grouped into three families:

References

^ The American Arachnological Society Committee on Common Names of Arachnids (2003). R.G. Breene (chair) (ed.). Common Names of Arachnids 2003 (PDF online publication) (5th ed.). Carlsbad, NM: American Tarantula Society. p. 42. ISBN 1-929427-11-5.
^ Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 615–617. ISBN 0-03-056747-5.
^ Humphreys, W.F., et al. (1989) The biology of Schizomus vinei (Chelicerata: Schizomida) in the caves of Cape Range, Western Australia. J. ZOol. Lond. 217: 177-201.

Reddell, J.R. & Cokendolpher, J.C. (1995). Catalogue, bibliography, and generic revision of the order Schizomida (Arachnida). Tex. Mem. Mus., Speleol. Monogr. 4: 1-170
Savory, T., 1977. Arachnida. second edition. Academic Press inc. New York. 339pp.

[1] The American Arachnological Society Committee on Common Names of Arachnids (2003). R.G. Breene (chair) (ed.). Common Names of Arachnids 2003 (PDF online publication) (5th ed.). Carlsbad, NM: American Tarantula Society. p. 42. ISBN 1-929427-11-5.

[IZ-2] Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 615–617. ISBN 0-03-056747-5.

[3] Humphreys, W.F., et al. (1989) The biology of Schizomus vinei (Chelicerata: Schizomida) in the caves of Cape Range, Western Australia. J. ZOol. Lond. 217: 177-201.

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