The Mygalomorphae, or mygalomorphs, are an infraorder of spiders, and comprise one of three major groups of living spiders with over 3000 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.
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.
Atracidae is a family of mygalomorph spiders, commonly known as Australian funnel-web spiders or atracids. It has been included as a subfamily of the Hexathelidae, but is now recognized as a separate family. All members of the family are native to Australia. Atracidae consists of three genera: Atrax, Hadronyche, and Illawarra, comprising 35 species. Some members of the family produce venom that is dangerous to humans, and bites by spiders of six of the species have caused severe injuries to victims. The bites of the Sydney funnel-web spider and northern tree-dwelling funnel-web spider are potentially deadly, but no fatalities have occurred since the introduction of modern first-aid techniques and antivenom.
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.
Xiphosura is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs. They first appeared in the Hirnantian. Currently, there are only four living species. Xiphosura contains one suborder, Xiphosurida, and several stem-genera.
The order Trigonotarbida is a group of extinct arachnids whose fossil record extends from the late Silurian to the early Permian. These animals are known from several localities in Europe and North America, as well as a single record from Argentina. Trigonotarbids can be envisaged as spider-like arachnids, but without silk-producing spinnerets. They ranged in size from a few millimetres to a few centimetres in body length and had segmented abdomens (opisthosoma), with the dorsal exoskeleton (tergites) across the backs of the animals' abdomens, which were characteristically divided into three or five separate plates. Probably living as predators on other arthropods, some later trigonotarbid species were quite heavily armoured and protected themselves with spines and tubercles. About seventy species are currently known, with most fossils originating from the Carboniferous coal measures.
Archaeidae, also known as assassin spiders and pelican spiders, is a spider family with about ninety described species in five genera. It contains small spiders, ranging from 2 to 8 millimetres long, that prey exclusively on other spiders. They are unusual in that they have "necks", ranging from long and slender to short and fat. The name "pelican spider" refers to these elongated jaws and necks used to catch their prey. Living species of Archaeidae occur in South Africa, Madagascar and Australia, with the sister family Mecysmaucheniidae occurring in southern South America and New Zealand.
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.
The evolution of spiders has been ongoing for at least 380 million years. The group's origins lie within an arachnid sub-group defined by the presence of book lungs ; the arachnids as a whole evolved from aquatic chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. There may be more than 120,000 species. Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. Both extant and fossil species are described annually by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion.
Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest that they form a clade (Dekatriata) with Eurypterida and Arachnida. Chasmataspidids are known sporadically in the fossil record through to the mid-Devonian, with possible evidence suggesting that they were also present during the late Cambrian. Chasmataspidids are most easily recognised by having an opisthosoma divided into a wide forepart (preabdomen) and a narrow hindpart (postabdomen) each comprising 4 and 9 segments respectively. There is some debate about whether they form a natural group.
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.
Spiders are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every land habitat. As of August 2022, 50,356 spider species in 132 families have been recorded by taxonomists. However, there has been debate among scientists about how families should be classified, with over 20 different classifications proposed since 1900.
This list of fossil arthropods described in 2015 is a list of new taxa of trilobites, fossil insects, crustaceans, arachnids and other fossil arthropods of every kind that have been described during the year 2015. The list only includes taxa at the level of genus or species.
Uraraneida is an extinct order of Paleozoic arachnids related to modern spiders. Two genera of fossils have been definitively placed in this order: Attercopus from the Devonian of United States and Permarachne from the Permian of Russia. Like spiders, they are known to have produced silk, but lack the characteristic spinnerets of modern spiders, and retain elongate telsons.
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.
Chimerarachne is a genus of extinct arachnids, containing a single species Chimerarachne yingi. Fossils of Chimerarachne were discovered in Burmese amber from Myanmar which dates to the mid-Cretaceous, about 100 million years ago. It is thought to be closely related to spiders, but outside any living spider clade. The earliest spider fossils are from the Carboniferous, requiring at least a 170 myr ghost lineage with no fossil record. The size of the animal is quite small, being only 2.5 millimetres (0.098 in) in body length, with the tail being about 3 millimetres (0.12 in) in length. These fossils resemble spiders in having two of their key defining features: spinnerets for spinning silk, and a modified male organ on the pedipalp for transferring sperm. At the same time they retain a whip-like tail, rather like that of a whip scorpion and uraraneids. Chimerarachne is not ancestral to spiders, being much younger than the oldest spiders which are known from the Carboniferous, but it appears to be a late survivor of an extinct group which was probably very close to the origins of spiders. It suggests that there used to be spider-like animals with tails which lived alongside true spiders for at least 200 million years.
Cretamygale is a genus of extinct mygalomorph spiders known from the Wessex Formation from the Isle of Wight, UK, dating the Barremian stage of the Early Cretaceous, around 128 million years ago. It contains only one species, C. chasei, known from a single specimen found in amber near Chilton Chine. It was tentatively assigned to the Nemesiidae in the original description. Later studies considered it indeterminate within the Avicularioidea.
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.
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.
Lagonomegopidae is an extinct family of spiders known from the Cretaceous period. Members of the family are distinguished by a large pair of eyes, positioned on the anterolateral flanks of the carapace, with the rest of the eyes being small. They have generally been considered members of Palpimanoidea, but this has recently been questioned. Members of the family are known from the late Early Cretaceous (Albian) to near the end of the Late Cretaceous (Campanian) of Eurasia, North America and the Middle East, which was then attached to Africa as part of Gondwana. They are generally assumed to have been free living hunters as opposed to web builders.
