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The Mygalomorphae (also called the Orthognatha) are an infraorder of spiders. The scientific name comes from the orientation of the fangs which point straight down and do not cross each other (as opposed to araneomorph). ==Description== This grouping of several families includes the heavy bodied, stout legged spiders popularly known as tarantulas as well as the Australian funnel-web spiders. Like the "primitive" suborder of spiders Mesothelae, they have two pairs of book lungs, and downward pointing chelicerae. Because of this, the two groups were once believed to be closely related. Later it was realized that the common ancestors of all spiders had these features (a state known as symplesiomorphy). Following the branching into the suborders of Mesothelae and Opisthothelae, the mygalomorphs retained them, while their fellow Opisthothelae members the araneomorphs evolved new "modern" features, including a cribellum and cross-acting fangs (Coddington & Levy, 1991). Almost all species of Mygalomorphae have eight eyes, however there are some with fewer (''Masteria lewisi'' has only six eyes). Their chelicerae and fangs are large and powerful, and have ample venom glands that lie entirely within their chelicerae. It is a notable indication of the effectiveness of these attributes that occasionally members of this suborder will even kill small fish, small mammals, and the like. However, only spiders of the Australian genus ''Atrax'' possess venom harmful to humans. While the world's biggest spiders are mygalomorphs—''Theraphosa blondi'' (Latreille, 1804) has a body length of 10 cm, and a leg span of 28 cm—some species are less than one millimeter long. Mygalomorphs are capable of spinning at least slightly adhesive silk, and some build elaborate capture webs that approach a meter in diameter (Coddington & Levy, 1991). Unlike Araneomorphae, which die after about a year, Mygalomorphae can live for up to 25 years, and some don't reach maturity until they are about six years old.〔(About Spiders )〕 Some flies in the family Acroceridae which are endoparasites of mygalomorphs may remain dormant in the book lungs for as long as 20 years before beginning their development and consuming the spider. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mygalomorphae」の詳細全文を読む スポンサード リンク
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