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).
Temporal range: Triassic to present
|Missulena bradleyi, a mouse spider|
|About 20 families|
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.
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. 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 north-east 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 future.
Actinopodidae is a family of mygalomorph spiders found in Australia and South America. It includes mouse spiders, whose bites, though rare, are considered medically significant and potentially dangerous.Antrodiaetidae
Antrodiaetidae, also known as folding trapdoor spiders, is a small spider family related to atypical tarantulas. They are found almost exclusively in the western and midwestern United States, from California to Washington and east to the Appalachian mountains. Exceptions include Antrodiaetus roretzi and Antrodiaetus yesoensis, which are endemic to Japan and are considered relict species. It is likely that two separate vicariance events led to the evolution of these two species.The three species of the former genus Atypoides are now included in the genus Antrodiaetus.Araneomorphae
The Araneomorphae (also called the Labidognatha) are an infraorder of spiders. They are distinguished by having chelicerae (fangs) that point diagonally forward and cross in a pinching action, in contrast to the Mygalomorphae (tarantulas and their close kin), where they point straight down. Most of the spiders that people encounter in daily life belong to the Araneomorphae.Atypical tarantula
Atypidae, also known as atypical tarantulas or purseweb spiders, is a spider family containing only three genera. They are accomplished ambush predators that spend most of their time in a sock-like, silken retreat on the ground from where they kill their prey.Barychelidae
Barychelidae, also known as brushed trapdoor spiders, is a spider family with about 300 species in 42 genera. Most spiders in this family build trapdoor burrows. For example, the 20 millimetres (0.79 in) long Sipalolasma builds its burrow in rotted wood, with a hinged trapdoor at each end. The 10 millimetres (0.39 in) long Idioctis builds its burrow approximately 5 centimetres (2.0 in) deep, just below the high tide level, sealing the opening with a thin trapdoor. Some species avoid flooding by plugging their burrows, while others can avoid drowning by trapping air bubbles within the hairs covering their bodies. Some members of this group have a rake on the front surface of their chelicerae used for compacting burrow walls. These spiders can run up glass like tarantulas, and some can stridulate, though it isn't audible to humans.Ctenizidae
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.Dipluridae
The family Dipluridae, known as curtain-web spiders (or confusingly with other distantly related ones as funnel-web tarantulas) 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.Dwarf tarantula
Dwarf tarantulas, also known as sheet funnel-web spiders are a type of spider from the family Mecicobothriidae. Dwarf tarantulas are one of several families of the sub-order Mygalomorphae; this larger group also includes the true tarantulas.Euctenizidae
The Euctenizidae (formerly Cyrtaucheniidae subfamily Euctenizinae) are a family of mygalomorph spiders. They are now considered to be more closely related to Idiopidae.Halonoproctidae
Halonoproctidae is a family of mygalomorph spiders, split off from the family Ctenizidae in 2018. Species in the family are widely distributed in North and Central America, Australasia, Asia, southern Europe and North Africa. One species is recorded from Venezuela in South America. They are relatively large, sombrely coloured spiders, that live in burrows with some kind of trapdoor.Hexathelidae
Hexathelidae is a family of mygalomorph spiders. It is one of a number of families and genera of spiders known as funnel-web spiders. In 2018, the family was substantially reduced in size by genera being moved to three separate families: Atracidae, Macrothelidae and Porrhothelidae. Atracidae includes the most venomous species formerly placed in Hexathelidae.Idiopidae
Idiopidae, also known as armored trapdoor spiders, is a family of mygalomorph spiders first described by Eugène Simon in 1889. They have a large body similar to tarantulas.Macrothele
Macrothele is a genus of mygalomorph spiders in the Macrothelidae family, and was first described by A. Ausserer in 1871. It is the only genus in the family Macrothelidae, and most species occur in Asia, from India to Japan, and Java, with four found in Africa, and two in Europe. The name is derived from Ancient Greek μακρός ("makro-"), meaning "big", and θηλή ("thele"), referring to the spinnerets.Microstigmatidae
Microstigmatidae is a small family of spiders with about 25 described species in eight genera. They are small ground-dwelling and free-living spiders that make little use of silk.The family was removed from the family Dipluridae in 1981. The subfamily Pseudonemesiinae from the Ctenizidae family was also transferred into the Microstigmatidae.Migidae
Migidae, also known as tree trapdoor spiders, is a family of spiders with about 100 species in eleven genera. They are small spiders with little to no hair and build burrows with a trapdoor. Some species live in tree fern stems. They have a Gondwanan distribution, found almost exclusively on the Southern Hemisphere, occurring in South America, Africa, Madagascar, Australia, New Zealand and New Caledonia.Nemesiidae
Nemesiidae, also known as funnel-web tarantulas, is a family of mygalomorph spiders first described by Eugène Simon in 1889, and raised to family status in 1985. Before becoming its own family, it was considered part of "Dipluridae". Fossils have been found dating this family back to the Lower Cretaceous.Opisthothelae
The Opisthothelae are spiders within the order Araneae, consisting of the Mygalomorphae and the Araneomorphae, but excluding the Mesothelae. The Opisthothelae are sometimes presented as an unranked clade and sometimes as a suborder of the Araneae. In the latter case, the Mygalomorphae and Araneomorphae are treated as infraorders.
The fairly recent creation of this taxon has been justified by the requirement to distinguish these spiders from the Mesothelae, which display many more primitive characteristics. Those that distinguish between the Mesothelae and Opisthothelae are:
The tergite plates on the abdomen of Mesothelae but absent in Opisthothelae
The almost total absence of ganglia in the abdomen of Opisthothelae
The almost median position of the spinnerets in the Mesothelae compared with the hindmost position of those of the OpistothelaeAmong the Opisthothelae, the fangs of the Mygalomorphae point straight down in front of the mouth aperture and only allow the spider to grasp its prey from above and below, whereas in the Araneomorphae, they face one another like pincers, allowing a firmer grip. Lampshade spiders (family Hypochilidae) show some characteristics of Araneomorphae despite being mygalomorphs and have fangs that can move diagonally. Distinguishing araneomorphs and mygalomorphs on first inspection is difficult unless the specimens are large enough to permit immediate examination of the fangs.Paratropididae
Paratropididae, also known as baldlegged spiders, is a small family of mygalomorph spiders first described by Eugène Simon in 1889. They are more closely related to tarantulas and allies, than to most other 'true' spiders (araneomorphs).Porrhothele
Porrhothele is a genus of South Pacific mygalomorph spiders in the Porrhothelidae family, and was first described by Eugène Louis Simon in 1892. Originally placed with the curtain web spiders, it was moved to the Hexathelidae in 1980, then to its own family in 2018.Members of Porrhothelidae are distinguished from other mygalomorph spiders by the small posterior sigillae and a single row of teeth on the forward-facing margin of the chelicerae. Males have a large number of strong spines on the forward-facing margin of their tibiae.
Extant Araneae families