Schizomida, also known as sprickets or short-tailed whip-scorpions, is an order of arachnids, generally less than in length. The order is not yet widely studied. E. O. Wilson has identified schizomids as among the "groups of organisms that desperately need experts to work on them."
Taxonomy
Schizomids are grouped into three families:
- Calcitronidae † (fossil; dubious)
- Hubbardiidae
- Protoschizomidae (2 genera, 15 species)
- Agastoschizomus
- <span class="feature-off feature-information"></span>Protoschizomus
About 300 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). The Schizomida is sister to the order Uropygi, the two clades together forming the Thelyphonida (in the broad sense of the name). Based on molecular clock dates, both orders likely originated in the late Carboniferous somewhere in the tropics of Pangea, and the Schizomida underwent substantial diversification starting in the Cretaceous.
Morphology
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 prosoma is divided into two separate plates.
thumb|Modified flagellum of male Hubbardia pentapeltis|260px
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. The females generally have three- or four-segmented flagella, while in males it is single segmented.
Like the related orders Uropygi and Amblypygi, and the more distantly related 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.
Schizomids have no actual eyes, but a few species have vestigial eyespots capable of telling light from dark. They breathe through a single pair of book lungs located on the second abdominal segment, as the second pair on third abdominal segment found in the other orders of Tetrapulmonata is lost.
Distribution and habitat
Schizomids are generally tropical and subtropical creatures, and they have a global distribution in these habitats, including in Southeast Asia, India, Australia, several Pacific Islands, Central and South America, and Africa. Additionally, some populations have been found in neighboring temperate regions such as California and Texas. Despite their global distribution, most schizomid species have very restricted distributions, with many only known from their original locality. Although most species are restricted to rainforests, they can also be found in neighboring woody areas.
Mortality and defense
Not much is known about the natural predators of sprickets.