Temporal range: Triassic to present
|Missulena bradleyi, a mouse spider|
|Infraorder:|| Mygalomorphae |
|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.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.
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.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.
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 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.
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. [ citation needed ]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.
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. The oldest known mygalomorph is Rosamygale grauvogeli (Hexathelidae) from the Triassic of northeastern France. No mygalomorphs from the Jurassic have yet been found.
The number of families and their relationships have both been undergoing substantial changes since a cladogram showing family relationships was published in 2005,with two significant studies in 2018. 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.
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.
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:
|Antrodiaetidae||4||37||folding trapdoor spiders||Atypoides riversi|
|Atypidae||3||54||atypical tarantulas or purseweb spiders||Sphodros rufipes (red legged purseweb spider)|
|Mecicobothriidae||1||2||dwarf tarantulas or sheet funnel-web spiders||Mecicobothrium thorelli|
|Actinopodidae||3||73||Missulena bradleyi (Eastern mouse spider)|
|Atracidae||3||35||Australian funnel-web spiders||Atrax robustus (Sydney funnel-web spider)|
|Barychelidae||42||294||Brushed trapdoor spiders||Sason sundaicum|
|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|
|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)|
|Macrothelidae||1||35||Macrothele calpeiana (Spanish funnel-web spider)|
|Microhexuridae||1||2||Microhexura montivaga (Spruce-fir moss spider)|
|Migidae||11||102||tree trapdoor spiders||Calathotarsus simoni|
|Paratropididae||5||17||baldlegged spiders||Paratropis tuxtlensis|
|Porrhothelidae||1||5||Porrhothele antipodiana (black tunnelweb spider)|
|Theraphosidae||147||991||tarantulas||Theraphosa blondi (Goliath birdeater)|
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)".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.
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.
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 Hexathelidae.
The spider family Liphistiidae, recognized by Tamerlan Thorell in 1869, comprises 8 genera and about 100 species of medium-sized spiders from Southeast Asia, China, and Japan. They are among the most basal living spiders, belonging to the suborder Mesothelae. In Japan, the Kimura spider is well known.
Ctenizidae is a small family of medium-sized mygalomorph spiders that construct burrows with a cork-like trapdoor made of soil, vegetation and silk. They may be called trapdoor spiders, as are similar species, such as those of the families Liphistiidae, Barychelidae, Cyrtaucheniidae and some species in Idiopidae and Nemesiidae. In 2018, the family Halonoproctidae was split off from Ctenizidae, leaving only three genera.
Spider taxonomy is that part of taxonomy that is concerned with the science of naming, defining and classifying all spiders, members of the Araneae order of the arthropod class Arachnida with about 46,000 described species. However, there are likely many species that have escaped the human eye to this day, and many specimens stored in collections waiting to be described and classified. It is estimated that only one third to one half of the total number of existing species have been described.
Stanwellia is a genus of South Pacific araneomorph 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 araneomorph 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.
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 araneomorph 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 three species, found in Namibia and South Africa: P. capensis, 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.
Spiroctenus is a genus of African araneomorph spiders in the family Bemmeridae. 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, and to the Bemmeridae in 2020. It is a senior synonym of Bemmeris, Bessia, and Ctenonemus.
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.
Pycnothelidae is a family of mygalomorph spiders first described in 1917. It was downgraded to a subfamily of the funnel-web trapdoor spiders in 1985, but returned to family status in 2020.
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, Optova 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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