Thelyphonida
Thelyphonida is an arachnid order comprising invertebrates commonly known as whip scorpions or vinegaroons (also spelled vinegarroons and vinegarones). They are often called uropygids in the scientific community based on an alternative name for the order, Uropygi (which may then also include the order Schizomida). The name "whip scorpion" refers to their resemblance to true scorpions 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.
Carl Linnaeus first described a whip scorpion in 1758, although he did not distinguish it from what are now regarded as different kinds of arachnid, calling it Phalangium caudatum. Phalangium is now used as a name for a genus of harvestmen (Opiliones). In 1802, Pierre André Latreille was the first to use a genus name solely for whip scorpions, namely Thelyphonus.[1][2] Latreille later explained the name as meaning "qui tue", meaning "who kills".[3][note 1] One name for the order, Thelyphonida, is based on Latreille's genus name. It was first used (with the spelling Thelyphonidea) by O. P. Cambridge in 1872.[4]
The name "uropygid" means "tail rump", from Ancient Greek οὐροπύγιον (ouropugion),[5] from οὐρά (oura) "tail" and πυγή (puge) "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), Thelyphonida 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.[6] The remainder has either continued to be called by the same name, Uropygi,[1] possibly distinguished as Uropygi sensu stricto, or called Thelyphonida.[6] Other sources do not accept the split, and continue to treat Schizomida as part of Uropygi.[7] Phylogenetic studies show the three orders to be closely related, and the older order names may now be used as names for clades, as shown below.[6][8] The Schizomida and Thelyphonida likely diverged in the late Carboniferous, somewhere in the tropics of Pangaea.[9]
Whip scorpions range from 25 to 85 mm (1.0 to 3.3 in) in length, with most species having a body no longer than 30 mm (1.2 in); the largest species, of the genus Mastigoproctus, can reach 85 mm (3.3 in).[10] 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).[11]
Like the related orders Schizomida and Amblypygi, the vinegaroons 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 pedipalps (pincers) but there is an additional large spine on each palpal tibia. They have one pair of eyes at the front of the cephalothorax and three on each side of the head, a pattern also found in scorpions.[10] Vinegaroons 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.[10] The acetic acid gives this spray a vinegar-like smell, giving rise to the common name vinegaroon.
