Uropygid
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[Photo] Picture taken by Justin Overholt of pet male whip scorpion. Date 22 November 2005. http://en.wikipedia.org/wiki/Image:Whipscorpion.jpg

A uropygid, commonly known as a Whip Scorpion, is an invertebrate animal belonging to the former order "Uropygi" in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. They are also known as the vinegarone or vinegaroon (in Spanish, vinagrillo) because when agitated they can spray a vinegar-like mist.

The name of the order should be properly Thelyphonida (a typified name), because the circumscriptional name Uropygi Thorell 1882 originally includes the "Tartarides" (now Schizomida) and should be used instead for the name of a broader group (which is also a well-recognized clade) including the Thelyphonida + Schizomida.

Physical description
The name "uropygid" means "tail rump", referring to the whip-like flagellum on the end of the pygidium, a small plate made up of the last three segments of the abdominal exoskeleton.

Whip scorpions range from 25 to 85 mm in length; the largest species, of the genus Mastigoproctus, reaching 85 mm.

Like the related orders Schizomida, Amblypygi, and Solifugae, the uropygids use only six legs for walking, having modified their first two legs to serve as antennae-like sensory organs. Many species also have very large scorpion-like pedipalps (pincers). They have one pair of eyes at the front of the cephalothorax and three on each side of the head. Whip scorpions have no poison glands, but they do have glands near the rear of their abdomen that can spray a combination of acetic acid and octanoic acid when they are bothered. The acetic acid gives this spray a vinegar-like smell, giving rise to the common name vinegaroon. Other species spray formic acid or chlorine.

Behaviour
Whip scorpions are carnivorous, nocturnal hunters feeding mostly on insects but sometimes on worms and slugs. The prey is crushed between special teeth on the inside of the trochanters (the second segment of the leg) of the front legs. They are valuable in controlling the population of roaches and crickets.

Males secrete a sperm sac, which is transferred to the female. Up to 35 eggs are laid in a burrow, within a mucous membrane that preserves moisture. Mothers stay with the eggs and do not eat. The white young that hatch from the eggs climb onto their mother's back and attach themselves there with special suckers. After the first molt they look like miniature whip scorpions, and leave the burrow; the mother dies soon after. The young grow slowly, going through three molts in about three years before reaching adulthood.

Habitat
Uropygids are found in tropical and subtropical areas worldwide, usually in underground burrows which they dig with their pedipalps. They may also burrow under logs, rotting wood, rocks, and other natural debris. They enjoy humid, dark places and avoid the light.

Subtaxa
As of 2006, over 100 species of uropygids have been described worldwide. Subtaxa of uropygids currently include only one extant family and a doubtful extinct family:

Thelyphonidae Lucas 1835

Hypoctoninae Pocock 1899 - Africa, India, SE Asia, Caribbean and South America
Mastigoproctinae Speijer 1933 [=Uroproctinae Rowland & Cooke 1973] - Caribbean, South America, Philippines, India
Thelyphoninae Lucas 1835 - SE Asia, Pacific islands.
Typopeltinae Rowland & Cooke 1973- Japan, China, SE Asia.

Geralinuridae Scudder 1886: fossil from Carboniferous, Czech Republic.

There are two more recently described fossil species of Thelyphonida:

Proschizomus petrunkevitchi Dunlop & Horrocks 1996 - upper Carboniferous, Great Britain.
Mesoproctus rowlandi Dunlop 1998 - lower Cretaceous, Brazil.

Rowland & Cooke (1973) provided a useful synopsis of the order, including a key to genera and a checklist of species. They also presented a novel classification that included the division of the group into two families, Thelyphonidae and Hypoctonidae. Weygoldt (1979) suggested that the existence of two families was not supported by the available data, and Haupt & Song (1996) formally reduced the Hypoctonidae to a subfamily as there was little support for a monophyletic Hypoctonidae. Dunlop & Horrocks (1996) suggested that the ‘‘hypoctonids’’ may be the sister-group to the Schizomida + Proschizomus Dunlop & Horrocks 1996, but the character polarities they utilized were regarded as uncertain and many features of Proschizomus were not observable in the fossilized material (Harvey, 2002).

http://en.wikipedia.org/wiki/Uropygid

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