These elements work the same way as in most other arachnids. As in most species, it holds its pedipalps clear of the ground its front legs serve as tactile sensors, barely touching the ground with their setae. Male solifuge in South African veld: Its flagella are visible near the tips of the chelicerae, looking like large, backward-curling bristles. As embryos they also have opisthosomal protuberances resembling the pulmonary sacs found in some palpigrades. 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. 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. Unlike scorpions, solifuges do not have a third tagma that forms a "tail".Ĭurrently, 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. The chelicerae serve as jaws and in many species also are used for stridulation. Meso- and metapeltidium contains the third and fourth pairs of legs. The propeltidium contains the eyes, the chelicerae that, in most species, are conspicuously large, the pedipalps and the first two pairs of legs. It is covered by a carapace, also called a prosomal dorsal shield or peltidium, which is composed of three distinct elements called propeltidium, mesopeltidium and metapeltidium. The prosoma comprises the head, the mouthparts, and the somites that bear the legs and the pedipalps. Spiders need considerable mobility of their abdomens in their spinning activities, and the Solifugae have no such adaptation. 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. 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 abdominal tergites and sternites are separated by large areas of intersegmental membranes, giving it a high degree of flexibility and ability to stretch considerably, which allows it to consume a large amount of food. 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. 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. More practical measurements refer primarily to the body length, quoting leg lengths separately, if at all. In practice, the respective lengths of the legs of various species differ drastically, so the resulting figures are often misleading. 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. Ventral aspect of a solifuge, showing respiratory slots
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