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Uropygi is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids. The name "whip scorpion" refers to their resemblance to scorpion and possession of a whiplike tail, and "vinegaroon" refers to their ability when attacked to discharge an offensive, vinegar-smelling liquid, which contains acetic acid. The order may also be called Thelyphonida. Both names, Uropygi and Thelyphonida, may be used either in a narrow sense for the order of whip scorpions, or in a broad sense which includes the order Schizomida.
The alternative name, Uropygi, was first used by Tamerlan Thorell in 1883. It means "tail rump", from Ancient Greek ( ouropygion), from ( oura) "tail" and ( pygē) "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.
The classification and scientific name used for whip scorpions varies. Originally, Amblypygi (whip spiders), Uropygi and Schizomida (short-tailed whipscorpions) formed a single order of arachnids, Pedipalpi. Pedipalpi was later divided into two orders, Amblypygi and Uropygi (or Uropygida). Schizomida was then split off from Uropygi into a separate order. The remainder has either continued to be called by the same name, Uropygi, possibly distinguished as Uropygi sensu stricto, or called Thelyphonida. When the name Uropygi is used for the whip scorpions, the clade containing Uropygi and Schizomida may be called Thelyphonida, or Thelyphonida sensu lato Conversely, when the name Thelyphonida is used for the whip scorpions alone, the parent clade may be called Uropygi, or Uropygi sensu lato. The table below summarizes the two usages. When the qualifications sensu lato and sensu stricto are omitted, the names Uropygi and Thelyphonida are ambiguous.
Phylogenetic studies show the three groups, Amblypygi, Uropygi sensu stricto and Schizomida, to be closely related. The Uropygi sensu stricto and Schizomida likely diverged in the late Carboniferous, somewhere in the tropics of Pangaea.
The opisthosoma consists of 12 segments. The first segment forms a pedicel, and each of the next eight segments has dorsal Tergum. The last three segments are fused into closed rings, forming a pygidium that ends with a flagellum of 30–40 units.
Like the related orders Schizomida and Amblypygi, whip scorpions use only six legs for walking, with the first two legs serving as antennae-like sensory organs. All species also have very large scorpion-like (pincers) but there is an additional large spine on each palpal tibia. They have one pair of median eyes at the front of the cephalothorax and up till five pairs of lateral eyes on each side of the head, a pattern also found in scorpions. Whip scorpions have no venom glands, but they have glands near the rear of their abdomen that can spray a combination of acetic acid and caprylic acid when they are bothered. The acetic acid gives this spray a vinegar-like smell, giving rise to the common name vinegaroon.
Males secrete a spermatophore (a united mass of sperm), which is transferred to the female following courtship behaviour, in which the male holds the ends of the female's first legs in his chelicerae. The spermatophore is deposited on the ground and picked up by the female using her genital area. In some genera, the male then uses his pedipalps to push the spermatophore into her body.
After a few months, the female will dig a large burrow and seal herself inside. Up to 40 eggs are , within a membranous broodsac that preserves moisture and remains attached to the genital operculum and the fifth segment of the mother's ventral opisthosoma. The female refuses to eat and holds her opisthosoma in an upward arch so that the broodsac does not touch the ground for the next few months, as the eggs develop into . Appendages become visible.
The white young that hatch from the postembryos climb onto their mother's back and attach themselves there with special suckers. After the first Moulting, when they look like miniature adults but with bright red palps, they leave the burrow. The mother may live up to two more years. The young grow slowly, going through four moults in about four years before reaching adulthood. They live for up to another four years.
They usually dig burrows with their pedipalps, to which they transport their prey. They may also burrow under logs, rotting wood, rocks, and other natural debris. They prefer humid, dark places and avoid light. Mastigoproctus giganteus, the giant whip scorpion, is found in more arid areas, including Arizona and New Mexico.
In addition, seven extinct genera were accepted, two within the family Thelyphonidae:
+ Alternative nomenclature Thelyphonidae Hubbardiidae, Protoschizomidae
Description
Whip scorpions range from in length, with most species having a body no longer than ; the largest species, of the genus Mastigoproctus, can reach . An extinct Mesoproctus from the Lower Cretaceous Crato Formation could be the same size. Because of their legs, claws, and "whip", though, they can appear much larger, and the heaviest specimen weighed was 12.4 grams (0.44 oz).
Behaviour
Whip scorpions are carnivorous, nocturnal hunters feeding mostly on , , scorpions, and terrestrial isopods, but sometimes on worms and slugs. Mastigoproctus sometimes preys on small . The prey is crushed between special teeth on the inside of the trochanters (the second segment of the "legs") of the front appendages. They are valuable in controlling the population of cockroaches and crickets.
Distribution and habitat
Whip scorpions are found in tropical and subtropical areas, excluding Europe and Australia. Also, only a single species is known from Africa: Etienneus africanus, probably a Gondwana relict, endemic to Senegal, the Gambia and Guinea-Bissau.
Subtaxa
As of 2023, the World Uropygi Catalog accepted the following 16 extant genera, all placed in the family Thelyphonidae:
and five unplaced as to family:
Notes
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