Mygalomorphae

The Mygalomorphae or mygalomorphs are an infraorder of spiders. The name is derived from the Greek mugalē, meaning "shrew", plus morphē meaning form or shape.[2] An older name for the group is Orthognatha, derived from the orientation of the fangs which point straight down and do not cross each other (as they do in the araneomorphs).

Mygalomorphs
Temporal range: Triassic to present
Mouse spider
Missulena bradleyi, a mouse spider
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Suborder: Opisthothelae
Infraorder: Mygalomorphae
Pocock, 1892[1]
Families

See text.

Diversity
About 20 families

Description

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 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.[3] Mesotheles retain the external abdominal segmentation of ancestral arachnids and have at least vestiges of four pairs of spinnerets, whereas mygalomorphs lack abdominal segmentation (like other opistotheles) and have a reduced number of spinnerets, often only two pairs.[4]

Like spiders in general, most species of Mygalomorphae have eight eyes, one pair of principal and three pairs of secondary eyes. But there are also species with six, four, two or no eyes.

Black Wishbone
Chelicerae of a black wishbone spider (Nemesiidae)

Their chelicerae and fangs are large and powerful and have ample venom glands that lie entirely within their chelicerae. These weapons, combined with their size and strength, make Mygalomorph spiders powerful predators. Many of these spiders are well adapted to killing other large arthropods and will also sometimes kill small mammals, birds, and reptiles. Despite their fearsome appearance and reputation, most mygalomorph spiders are not harmful to humans, with the exception of the Australian funnel-web spiders, especially those of the genus Atrax.

While the world's biggest spiders are mygalomorphs —Theraphosa blondi has a body length of 10 cm (3.9 in) and a leg span of 28 cm (11 in)—some species are less than one millimeter (0.039 in) long. Mygalomorphs are capable of spinning at least slightly adhesive silk, and some build elaborate capture webs that approach a meter in diameter.[3]

Unlike Araneomorphae, which die after about a year, Mygalomorphae can live for up to 25 years, and some do not reach maturity until they are about six years old.[5] Some flies in the family Acroceridae that are endoparasites of mygalomorphs may remain dormant in their book lungs for as long as 20 years before beginning their development and consuming the spider.

One female trapdoor spider, first recorded in a survey in 1974 in Western Australia, is known to have lived for 43 years.[6]

Taxonomy

Evolution and phylogeny

Megarachne servinei was thought to be a giant mygalomorph from the Upper Carboniferous (ca. 350 million years ago), but was later found to be an eurypterid.[7] Thus, the oldest known mygalomorph is Rosamygale grauvogeli (Hexathelidae) from the Triassic of north-east France. No mygalomorphs from the Jurassic have yet been found.[8]

The number of families and their relationships have both been undergoing substantial changes since a cladogram showing family relationships was published in 2005,[9] with two significant studies in 2018.[10][11] The division of Mygalomorphae into two superfamilies, Atypoidea and Avicularioidea, has been established in many studies. The Atypoidea retain some vestiges of abdominal segmentation in the form of dorsal tergites; the Avicularioidea lack these. Molecular phylogenetic studies undertaken between 2012 and 2017 have found somewhat different relationships within the Avicularioidea. Some families appear not to be monophyletic and further changes are possible in future.[4]

Families

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 species occur in Europe. These are of the families Atypidae, Nemesiidae, Ctenizidae, Macrothelidae, Theraphosidae and Cyrtaucheniidae, together with only a dozen species.

However, it is suggested that the Mygalomorphae were distributed worldwide before the breakup of Pangaea.[8]

References

  1. ^ Dunlop, Jason A. & Penney, David (2011). "Order Araneae Clerck, 1757" (PDF). In Zhang, Z.-Q. Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness. Zootaxa. Auckland, New Zealand: Magnolia Press. ISBN 978-1-86977-850-7. Retrieved 2015-10-31.
  2. ^ "mygalomorph". Oxford Dictionaries. Retrieved 2016-02-02.
  3. ^ a b Coddington, Jonathan A. & Levi, Herbert W. (1991). "Systematics and evolution of spiders (Araneae)". Annual Review of Ecology and Systematics: 565–592. doi:10.1146/annurev.es.22.110191.003025. JSTOR 2097274.
  4. ^ a b c d Wheeler, Ward C.; Coddington, Jonathan A.; Crowley, Louise M.; Dimitrov, Dimitar; Goloboff, Pablo A.; Griswold, Charles E.; Hormiga, Gustavo; Prendini, Lorenzo; Ramírez, Martín J.; Sierwald, Petra; Almeida-Silva, Lina; Alvarez-Padilla, Fernando; Arnedo, Miquel A.; Benavides Silva, Ligia R.; Benjamin, Suresh P.; Bond, Jason E.; Grismado, Cristian J.; Hasan, Emile; Hedin, Marshal; Izquierdo, Matías A.; Labarque, Facundo M.; Ledford, Joel; Lopardo, Lara; Maddison, Wayne P.; Miller, Jeremy A.; Piacentini, Luis N.; Platnick, Norman I.; Polotow, Daniele; Silva-Dávila, Diana; Scharff, Nikolaj; Szűts, Tamás; Ubick, Darrell; Vink, Cor J.; Wood, Hannah M. & Zhang, Junxia (2016), "The spider tree of life: phylogeny of Araneae based on target-gene analyses from an extensive taxon sampling", Cladistics, doi:10.1111/cla.12182
  5. ^ "About Spiders". CSIRO. Retrieved 2017-02-18.
  6. ^ World's oldest spider dies aged 43 in Western Australia ABC News, 28 April 2018. Retrieved 2018-04-29.
  7. ^ Selden, P.A.; Corronca, J.A. & Hünicken, M.A. (2005). "The true identity of the supposed giant fossil spider Megarachne". Biology Letters. 1: 44–48. doi:10.1098/rsbl.2004.0272. PMC 1629066Freely accessible.
  8. ^ a b Selden, P.A.; da Costa Casado, F. & Vianna Mesquita, M. (2005). "Mygalomorph spiders (Araneae: Dipluridae) from the Lower Cretaceous Crato Lagerstätte, Araripe Basin, North-east Brazil". Palaeontology. 49 (4): 817–826. doi:10.1111/j.1475-4983.2006.00561.x.
  9. ^ Coddington, Jonathan A. (2005). "Phylogeny and classification of spiders" (PDF). In Ubick, D.; Paquin, P.; Cushing, P.E. & Roth, V. Spiders of North America: an identification manual. American Arachnological Society. pp. 18–24. Retrieved 2015-09-24.
  10. ^ a b c d Hedin, Marshal; Derkarabetian, Shahan; Ramírez, Martín J.; Vink, Cor & Bond, Jason E. (2018), "Phylogenomic reclassification of the world's most venomous spiders (Mygalomorphae, Atracinae), with implications for venom evolution", Scientific Reports, 8 (1): 1636, doi:10.1038/s41598-018-19946-2, retrieved 2018-05-20
  11. ^ a b Godwin, Rebecca L.; Opatova, Vera; Garrison, Nicole L.; Hamilton, Chris A. & Bond, Jason E. (2018), "Phylogeny of a cosmopolitan family of morphologically conserved trapdoor spiders (Mygalomorphae, Ctenizidae) using Anchored Hybrid Enrichment, with a description of the family, Halonoproctidae Pocock 1901", Molecular Phylogenetics and Evolution, 126: 303–313, doi:10.1016/j.ympev.2018.04.008, ISSN 1055-7903, retrieved 2018-05-20

Bibliography

  • Raven, R.J. (1985). The spider infraorder Mygalomorphae: Cladistics and systematics. Bull. Am. Mus. Nat. Hist. 182:1-180.
  • Goloboff, P.A. (1993). A Reanalysis of Mygalomorphae Spider Families (Araenae). American Museum Novitates 3056. PDF

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