Mygalomorphae

For the racing car manufacturer, see Mygale. For the novel by Thierry Jonquet, see Mygale (novel).

Mygalomorphae Temporal range: Triassic to present
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

The Mygalomorphae, or mygalomorphs, are an infraorder of spiders. The name is derived from the Greek mygalē, 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). In 1802, Charles Athanase Walckenaer separated mygalomorph spiders into a separate genus, Mygale, leaving all other spiders in Aranea.

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.

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 .^{[ citation needed ]}

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.^{[ citation needed ]}

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

Sphodros rufipes , an atypical mygyalomorph

Megarachne servinei was thought to be a giant mygalomorph from the Upper Carboniferous (about 350 million years ago), but was later found to be a eurypterid. ^[7] The oldest known mygalomorph is Rosamygale grauvogeli (Hexathelidae) from the Triassic of northeastern 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 the future. ^[4]

Mygalomorphae tend to be very morphologically conserved, which makes it difficult to find reliable morphological features to use in taxonomy. It has been hypothesized that because Mygalomorphae 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. ^[12]

Phylogeny

The relationships of taxa in the Mygalomorphae were restructured based on a comprehensive phylogenetic study by Opatova et al. (2020) ^[13] 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: ^[13]

Mygalomorphae

Atypoidea   Hexurellidae       Mecicobothriidae       Atypidae       Megahexuridae     Antrodiaetidae           Avicularioidea   Ischnothelidae       Microhexuridae         Hexathelidae     Euagridae         Porrhothelidae       Macrothelidae   Bipectina   Paratropididae           Stasimopidae   Venom Clade   Atracidae     Actinopodidae       Domiothelina   Halonoproctidae       Migidae       Idiopidae       Ctenizidae     Euctenizidae             Crassitarsae Theraphosoidina   Bemmeridae       Barychelidae     Theraphosidae       "Nemesioidina"   Nemesiidae       Pycnothelidae         Dipluridae     Cyrtaucheniidae         Anamidae       Entypesidae     Microstigmatidae

Families

Key

Genera	1	≥2	≥10	≥100
Species	1–9	≥10	≥100	≥1000

Mygalomorphae families ^{[note 1]}

Family	Genera	Species	Common name	Example
Atypoidea: [4]
Antrodiaetidae	4	37	folding trapdoor spiders	Atypoides riversi
Atypidae	3	54	atypical tarantulas or purseweb spiders	Sphodros rufipes (red legged purseweb spider)
Hexurellidae	1	4		Hexurella pinea
Mecicobothriidae	1	2	dwarf tarantulas or sheet funnel-web spiders	Mecicobothrium thorelli
Megahexuridae	1	1		Megahexura fulva
Avicularioidea: [4]
Actinopodidae	3	73		Missulena bradleyi (Eastern mouse spider)
Anamidae	9	85		Aname atra
Atracidae	3	35	Australian funnel-web spiders	Atrax robustus (Sydney funnel-web spider)
Barychelidae	42	294	Brushed trapdoor spiders	Sason sundaicum
Bemmeridae	2	35		Spiroctenus personatus
Ctenizidae	2	5	cork-lid trapdoor spiders	Cteniza sauvagesi
Cyrtaucheniidae	8	107	wafer trapdoor spiders	Fufius lucasae
Dipluridae	8	93	Curtain-web spiders	Diplura lineata
Entypesidae	3	37		Entypesa andohahela
Euagridae	12	81		Euagrus formosanus
Euctenizidae	7	76		Aptostichus simus
Halonoproctidae	6	93		Bothriocyrtum californicum (California trapdoor spider)
Hexathelidae	7	45	(Australian) funnel-web spiders	Hexathele hochstetteri
Idiopidae	22	407	armored trapdoor spiders	Idiosoma nigrum (black rugose trapdoor spider)
Ischnothelidae	5	26		Ischnothele caudata
Macrothelidae	1	35		Macrothele calpeiana (Spanish funnel-web spider)
Microhexuridae	1	2		Microhexura montivaga (Spruce-fir moss spider)
Microstigmatidae	12	41		Envia garciai
Migidae	11	102	tree trapdoor spiders	Calathotarsus simoni
Nemesiidae	24	195		Amblyocarenum nuragicus
Paratropididae	5	17	baldlegged spiders	Paratropis tuxtlensis
Porrhothelidae	1	5		Porrhothele antipodiana (black tunnelweb spider)
Pycnothelidae	6	81		Stanwellia hoggi
Stasimopidae	1	47		Stasimopus mandelai
Theraphosidae	147	991	tarantulas	Theraphosa blondi (Goliath birdeater)

Historical classification

In 1985, Robert Raven published a monograph of the Mygalomorphae in which he proposed an internal classification for the Mygalomorphae, based on morphological features. In 2020, Opatova et. al. commented "In short, much of today’s classification scheme dates back to Raven (1985)". ^[13] Raven used various compound ranks, such as "gigapicoorder" and "hyperpicoorder". Ignoring these unusual rank names, his classification can be shown diagrammatically: ^[15]

Tuberculotae Mecicobothrioidina   Mecicobothriidae     Microstigmatidae     Orthopalpae Hexatheloidina Hexathelidae   Quadrithelina Dipluroida Dipluridae   Crassitarsae Nemesioida Nemesiidae   Theraphosoidina Superfamily Theraphosoidea   Theraphosidae     Paratropididae     Superfamily Barycheloidea Barychelidae             Fornicephalae Atypoidina   Atypidae     Antrodiaetidae     Rastelloidina Cyrtaucheniina Cyrtaucheniidae   Domiothelina Idiopina Idiopidae   Ctenizoidina Superfamily Ctenizoidea Ctenizidae   Superfamily Migoidea   Migidae     Actinopodidae

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. ^[13]

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 range, currently, 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. (ed.). 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. Archived from the original on 2016-05-21. Retrieved 2016-02-02.
3. Coddington, Jonathan A. & Levi, Herbert W. (1991). "Systematics and evolution of spiders (Araneae)". Annual Review of Ecology and Systematics. 22: 565–592. doi:10.1146/annurev.es.22.110191.003025. JSTOR   2097274. S2CID   55647804.
4. Wheeler, Ward C.; Coddington, Jonathan A.; Crowley, Louise M.; Dimitrov, Dimitar; Goloboff, Pablo A.; Griswold, Charles E.; et al. (2016). "The spider tree of life: Phylogeny of Araneae based on target-gene analyses from an extensive taxon sampling". Cladistics. 33 (6): 574–616. doi:10.1111/cla.12182. S2CID   35535038.
5. "About Spiders". CSIRO. Archived from the original on 2015-09-24. Retrieved 2017-02-18.
6. World's oldest spider dies aged 43 in Western Australia Archived 2018-04-29 at the Wayback Machine 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 (1): 44–48. doi:10.1098/rsbl.2004.0272. PMC   1629066 . PMID   17148124.
8. 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. hdl: 1808/8355 .
9. Coddington, Jonathan A. (2005). "Phylogeny and classification of spiders" (PDF). In Ubick, D.; Paquin, P.; Cushing, P.E. & Roth, V. (eds.). Spiders of North America: an identification manual. American Arachnological Society. pp. 18–24. Retrieved 2015-09-24.
10. 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. PMC   5785998 . PMID   29374214.
11. 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. PMID   29656103.
12. Bond, Jason E.; Hedin, Marshal (1 October 2006). "A total evidence assessment of the phylogeny of North American euctenizine trapdoor spiders (Araneae, Mygalomorphae, Cyrtaucheniidae) using Bayesian inference". Molecular Phylogenetics and Evolution. 41 (1): 70–85. doi:10.1016/j.ympev.2006.04.026. ISSN   1055-7903. PMID   16857391.
13. Opatova, Vera; Hamilton, Chris A.; Hedin, Marshal; Montes De Oca, Lauren; Král, Jiři; Bond, Jason E. (16 October 2019). "Phylogenetic Systematics and Evolution of the Spider Infraorder Mygalomorphae Using Genomic Scale Data". Systematic Biology. 69 (4): 671–707. doi:10.1093/sysbio/syz064. PMID   31841157.
15. Raven, Robert J. (1985). "The spider infraorder Mygalomorphae (Araneae) : cladistics and systematics". Bulletin of the American Museum of Natural History. 182 (1): 1–180.

Notes

1. Unless otherwise shown, currently accepted families and counts based on the World Spider Catalog version 19.0 as of 11 July 2018 ^[update] . ^[14] In the World Spider Catalog, "species" counts include subspecies. Assignment to sub- and infraorders based on Coddington (2005, p. 20) (when given there).

Bibliography

• Raven, R.J. (1985). "The spider infraorder Mygalomorphae: Cladistics and systematics". Bulletin of the American Museum of Natural History. 182: 1–180.
• Goloboff, Pablo A. (23 March 1993). A reanalysis of Mygalomorphae spider families (Araenae) (PDF) (Report). American Museum Novitates. New York, NY: American Museum of Natural History.

External links

Wikispecies has information related to Mygalomorphae

Wikimedia Commons has media related to Mygalomorphae .

• Taxonomy, husbandry and captive breeding of Dipluridae
• Mygalomorphae or primitive spiders
• Suborder Mygalomorphae