Solifugae
Solifugae is an order of animals in the class Arachnida known variously as camel spiders, wind scorpions, sun spiders, or solifuges. The order includes more than 1,000 described species in about 147 genera. Despite the common names, they are neither true scorpions (order Scorpiones) nor true spiders (order Araneae). Most species of Solifugae live in dry climates and feed opportunistically on ground-dwelling arthropodsand other small animals. The largest species grow to a length of 12–15 cm (5–6 in), including legs. A number of urban legends exaggerate the size and speed of the Solifugae, and their potential danger to humans, which is negligible.
Solifuges are moderately small to large arachnids (a few millimeters to several centimeters in body length), with the larger species reaching 12–15 cm (5–6 in) in length, including legs.[2][3] In practice, the respective lengths of the legs of various species differ drastically, so the resulting figures are often misleading. More practical measurements refer primarily to the body length, quoting leg lengths separately, if at all. The body length is up to 7 cm (3 in).[4][5] Most species are closer to 5 cm (2 in) long, and some small species are under 1 cm (0.4 in) in head-plus-body length when mature.[6]
Like that of the spider order, the Araneae, the body plan of the Solifugae has two main tagmata: the prosoma, or cephalothorax, is the anterior tagma, and the 10-segmented abdomen, or opisthosoma, is the posterior tagma. As shown in the illustrations, the solifuge prosoma and opisthosoma are not separated by nearly as clear a constriction and connecting tube or "pedicel" as occurs in Araneae. The lack of the pedicel reflects another difference between the Solifugae and spiders, namely that solifuges lack both spinnerets and silk, and do not spin webs. Spiders need considerable mobility of their abdomens in their spinning activities, and the Solifugae have no such adaptation.
The prosoma comprises the head, the mouthparts, and the somites that bear the legs and the pedipalps. Though it is not split into two clear tagmata, the prosoma does have a large, relatively well-defined anterior carapace, bearing the animal's eyes and two chelicerae that, in most species, are conspicuously large, while a smaller posterior section bears the pedipalps and legs.[6][7] The chelicerae serve as jaws and in many species also are used for stridulation. Unlike scorpions, solifuges do not have a third tagma that forms a "tail".
Currently, neither fossil nor embryological evidence shows that arachnids ever had a separate thorax-like division, so the validity of the term cephalothorax, which means a fused cephalon, or head, and thorax, has been questioned. Also, arguments exist against use of "abdomen", as the opisthosoma of many arachnids contains organs atypical of an abdomen, such as a heart and respiratory organs.[8]
Like other arachnids outside the orders of scorpions and the Tetrapulmonata, the Solifugae lack book lungs, having instead a well-developed tracheal system that inhales and exhales air through a number of spiracles - one pair between the second and third pair of walking legs, two pairs on the abdomen on abdominal segments three and four, and an unpaired spiracle on the fifth abdominal segment.[9] As embryos they also have opisthosomal protuberances resembling the pulmonary sacs found in some palpigrades.[10]
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