The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3,000 species, found on all continents except Antarctica. Many members are known as trapdoor spiders due to their creation of trapdoors over their burrows. Other prominent groups include Australian funnel web spiders and tarantulas, with the latter accounting for around one third of all mygalomorphs.
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.[2] 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.[3]
Like spiders in general, most species of Mygalomorphae have eight eyes, one pair of principal and three pairs of secondary eyes.
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 10cm (3.9in) and a leg span of 28cm (11in) – some species are less than one millimeter (0.039in) long. Mygalomorphs are capable of spinning at least slightly adhesive silk, and some build elaborate capture webs that approach a metre in diameter.[2]
Unlike Araneomorphae, which die after about a year, Mygalomorphae can live for up to 25years, and some do not reach maturity until they are about six years old.[4] Some flies in the family Acroceridae that are endoparasites of mygalomorphs may remain dormant in their book lungs for as long as 20years 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 43years.[5]
Taxonomy
The name is derived from the Greekmygalē, meaning "shrew", plus morphē meaning form or shape.[6] 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).
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.[3]Rosamygale belongs to Avicularioidea, based on the absence of an abdominal scutum and well-separated posterior lateral spinnerets.[12]
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.[13]
Phylogeny
The relationships of taxa in the Mygalomorphae were restructured based on a comprehensive phylogenetic study by Opatova et al. (2020)[14] 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:[14]
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)".[14] Raven used various compound ranks, such as "gigapicoorder" and "hyperpicoorder". Ignoring these unusual rank names, his classification can be shown diagrammatically:[16]
Tuberculotae
Mecicobothrioidina
Mecicobothriidae
Microstigmatidae
Orthopalpae
Hexatheloidina
Hexathelidae
Quadrithelina
Dipluroida
Dipluridae
Crassitarsae
Nemesioida
Nemesiidae
Theraphosoidina
SuperfamilyTheraphosoidea
Theraphosidae
Paratropididae
SuperfamilyBarycheloidea
Barychelidae
Fornicephalae
Atypoidina
Atypidae
Antrodiaetidae
Rastelloidina
Cyrtaucheniina
Cyrtaucheniidae
Domiothelina
Idiopina
Idiopidae
Ctenizoidina
SuperfamilyCtenizoidea
Ctenizidae
SuperfamilyMigoidea
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.[14]
Despite their limited current range, it is suggested that the Mygalomorphae were distributed worldwide before the breakup of Pangaea.[8]
Explanatory notes
↑ Unless otherwise shown, currently accepted families and counts based on the World Spider Catalog version 23.5 as of 8August2022[update].[15] In the World Spider Catalog, "species" counts include subspecies. Assignment to sub- and infraorders based on Coddington (2005, p.20) (when given there).
Citations
↑ 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. ISBN978-1-86977-850-7. Retrieved 2015-10-31.
1 2 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. S2CID3845623.
↑ 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.
↑ 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. ISSN1055-7903. PMID29656103. S2CID4890400.
The family Dipluridae, known as curtain-web spiders are a group of spiders in the infraorder Mygalomorphae, that have two pairs of booklungs, and chelicerae (fangs) that move up and down in a stabbing motion. A number of genera, including that of the Sydney funnel-web spider (Atrax), used to be classified in this family but have now been moved to Atracidae.
The Mesothelae are a suborder of spiders that includes a single extant family, Liphistiidae, and a number of extinct families. This suborder is thought to form the sister group to all other living spiders, and to retain ancestral characters, such as a segmented abdomen with spinnerets in the middle and two pairs of book lungs. Members of Liphistiidae are medium to large spiders with eight eyes grouped on a tubercle. They are found only in China, Japan, and southeast Asia. The oldest known Mesothelae spiders are known from the Carboniferous, over 300 million years ago.
Ctenizidae is a small family of mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation, and silk. They may be called trapdoor spiders, as are other, similar species, such as those of the families Liphistiidae, Barychelidae, and Cyrtaucheniidae, and some species in the Idiopidae and Nemesiidae. The name comes from the distinctive behavior of the spiders to construct trapdoors, and ambush prey from beneath them.
The family Cyrtaucheniidae, known as wafer-lid trapdoor spiders, are a widespread family of Mygalomorphae spiders.
Opisthothelae is a suborder of spiders within the order Araneae, containing Mygalomorphae and Araneomorphae, but excluding Mesothelae. The Opisthothelae are sometimes presented as an unranked clade and sometimes as a suborder of Araneae. In the latter case, Mygalomorphae and Araneomorphae are treated as infraorders.
Stanwellia is a genus of South Pacific mygalomorph spiders in the family Pycnothelidae. It was first described by W. J. Rainbow & R. H. Pulleine in 1918. Originally placed with the curtain-web spiders, it was transferred to the funnel-web trapdoor spiders in 1985, then to the Pycnothelidae in 2020. It is a senior synonym of Aparua.
The Euctenizidae are a family of mygalomorph spiders. They are now considered to be more closely related to Idiopidae.
Entychides is a genus of mygalomorph trapdoor spiders in the family Euctenizidae, and was first described by Eugène Simon in 1888. Originally placed with the Ctenizidae, it was moved to the wafer trapdoor spiders in 1985, then to the Euctenizidae in 2012.
Homostola is a genus of African mygalomorph spiders in the family Bemmeridae. It was first described by Eugène Louis Simon in 1892. Originally placed with the Ctenizidae, it was transferred to the wafer trapdoor spiders in 1985, and to the Bemmeridae in 2020. It is a senior synonym of Stictogaster and Paromostola.
Rhytidicolus is a monotypic genus of South American wafer trapdoor spiders containing the single species, Rhytidicolus structor. It was first described by Eugène Simon in 1889, and has only been found in Venezuela. Originally placed with the Ctenizidae, it was moved to the Cyrtaucheniidae in 1985 and Rhytidicolidae in 2022.
Entypesa is a genus of African mygalomorph spiders in the family Entypesidae. It was first described by Eugène Louis Simon in 1902. Originally placed with the curtain-web spiders, it was transferred to the funnel-web trapdoor spiders in 1985, then to the Entypesidae in 2020. It is a senior synonym of Pseudohermacha.
Hermacha is a genus of mygalomorphae spiders in the family Entypesidae. It was first described by Eugène Louis Simon in 1889. Originally placed with the Ctenizidae, it was transferred to the funnel-web trapdoor spiders in 1985, then to the Entypesidae in 2020. It is a senior synonym of Damarchodes and Hermachola.
Pionothele is a genus of African mygalomorph spiders in the family Pycnothelidae. It was first described by William Frederick Purcell in 1902. As of June 2020 it contains 2 species, found in Namibia and South Africa: P. gobabeb, and P. straminea. Originally placed with the Ctenizidae, it was transferred to the funnel-web trapdoor spiders in 1985, then to the Pycnothelidae in 2020.
Avicularioidea is a clade of mygalomorph spiders, one of the two main clades into which mygalomorphs are divided. It has been treated at the rank of superfamily.
Euagridae is a family of mygalomorph spiders. The group was first described as a tribe in 1979 by Robert Raven, who in 1985 elevated it to a subfamily. In 2020, Opatova et al. elevated it further to a family.
Bipectina is a clade of avicularioid mygalomorph spiders first proposed by Pablo A. Goloboff in 1993, based on a morphological cladistic analysis. The clade was marked by a number of morphological features, and in particular by the presence of two rows of teeth on the superior tarsal claws of the legs of both sexes, meaning that the claws were bipectinate. The clade was supported by some subsequent analyses, although not all. A major phylogenetic study in 2020 upheld the monophyly of the clade, which contained 19 of the 25 accepted families of the Avicularioidea.
Domiothelina is a clade of avicularioid mygalomorph spiders first proposed by Robert J. Raven in 1985, based on a morphological cladistic analysis. Raven characterized the clade by a number of shared features, including the domed apical segment of the posterior lateral spinnerets. The clade has been supported to some degree by subsequent molecular analyses, although with a somewhat different composition.
Crassitarsae is a clade of avicularioid mygalomorph spiders first proposed by Robert J. Raven in 1985, based on a morphological cladistic analysis. Raven characterized the clade by a number of shared features, including the presence of some scopulae on the tarsi. The clade has been supported to some degree by subsequent molecular analyses, although with a somewhat different composition.
Theraphosoidina is a clade of avicularioid mygalomorph spiders first proposed by Robert J. Raven in 1985, based on a morphological cladistic analysis. Raven included three families: Theraphosidae, Paratropididae and Barychelidae. Subsequent molecular phylogenetic studies upheld the relationship between the Theraphosidae and Barychelidae, but found that Paratropidae fell outside the clade.
Nemesioidina is a clade of avicularioid mygalomorph spiders proposed in 2020, based on a molecular phylogenetic analysis.
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