Mygalomorphae

This group of spiders comprises mostly heavy-bodied, stout-legged spiders including tarantulas, Australian funnel-web spiders, mouse spiders, and various families of spiders commonly called trapdoor 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 realised 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. One female trapdoor spider, first recorded in a survey in 1974 in Western Australia, is known to have lived for 43 years. ==Taxonomy==

The name is derived from the Greek mygalē, meaning "shrew", plus morphē meaning form or shape. Mygalomorphae tend to be highly morphologically conserved, which makes it difficult to find reliable morphological features to use for taxonomy. It has been hypothesized that because Mygalomorphae all tend to be fossorial and live in tubular webs, they are subjected to similar selective pressures, so most species should evolve in similar ways. Additionally, this may also mean that homoplasies are more likely to occur, further complicating taxonomy based on morphology. Phylogeny The relationships of taxa in the Mygalomorphae were restructured based on a comprehensive phylogenetic study by Opatova et al. (2020) The generic composition of the families Ctenizidae, Cyrtaucheniidae, Dipluridae, and Nemesiidae were relimited. Five subfamilies were raised to the rank of family: Anamidae, Euagridae, Ischnothelidae, Pycnothelidae, and Bemmeridae. Three new families were created: Entypesidae, Microhexuridae, and Stasimopidae. Lastly, a new subfamily, Australothelinae, was generated and placed in the family Euagridae. The preferred cladogram from Optova et al. (2020) is: }} Families Historical classification In 1802, C. A. Walckenaer separated mygalomorph spiders into a separate genus, Mygale, leaving all other spiders in Aranea In 1985, Robert Raven published a monograph of the Mygalomorphae in which he proposed an internal classification for the Mygalomorphae, based on morphological features. Opatova et al. (2020) commented "In short, much of today's classification scheme dates back to Raven (1985)". Raven used various compound ranks, such as "gigapicoorder" and "hyperpicoorder". Ignoring these unusual rank names, his classification can be shown diagrammatically: }} Subsequent research, largely based on molecular phylogenetic studies, has not upheld some of Raven's groupings. In particular his primary division between Tuberculotae and Fornicephalae has been replaced by a very different division between Atypoidea (expanded from Raven's Atypoidina) and Avicularioidea, which has no counterpart in his system. As another example, the families Mecicobothriidae and Microstigmatidae, which Raven placed in Mecicobothrioidina (a "gigapicoorder"), are now placed very far apart in the Atypoidea and Avicularioidea respectively. Other groups, such as Crassitarsae and Domiothelina, are more recognizable, allowing for some changes in family circumscriptions. ==Distribution==

Most members of this infraorder occur in the tropics and subtropics, but their range can extend farther north, e.g. into the southern and western regions of the United States. Only a few occur in Europe: 12 species from the families Atypidae, Nemesiidae, Ctenizidae, Macrothelidae, Theraphosidae, and Cyrtaucheniidae. Despite their limited current range, it is suggested that the Mygalomorphae were distributed worldwide before the breakup of Pangaea. == Footnotes ==