The Opiliones are an order of arachnids colloquially known as harvestmen, harvesters, or daddy longlegs. As of April 2017, over 6,650 species of harvestmen have been discovered worldwide, although the total number of extant species may exceed 10,000. The order Opiliones includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi, which were named in 2014.
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 sometimes called horseshoe crabs. They first appeared in the Hirnantian. Currently, there are only four living species. Xiphosura contains one suborder, Xiphosurida, and several stem-genera.
Arthrolycosidae is an extinct family of arachnids, possibly spiders. Fossils placed in the family were found in the Carboniferous to Permian, 359 to 252 million years ago. They were considered by Alexander Petrunkevitch to be "mesotheles", i.e. placed in the spider suborder Mesothelae. However, Paul A. Selden has stated they only have "the general appearance of spiders", with segmented abdomens (opisthosomae), but no definite spinnerets. At least some of the specimens placed in the family in the genus Arthrolycosa are considered to be spiders, whereas Eocteniza is "rather problematic as a spider".
The Arthromygalidae are an extinct family of arachnids, possibly spiders. Fossils placed in the family were all found in the Carboniferous, 359 to 299 million years ago. They were considered by Alexander Petrunkevitch to be "mesotheles", i.e. placed in the spider suborder Mesothelae. Petrunkevitch used the family for Carboniferous fossils he regarded as mesotheles but which lacked eyes. Paul A. Selden has shown the fossil specimens only have "the general appearance of spiders", with segmented abdomens (opisthosomae), but no definite spinnerets.
Plesiosiro is an extinct arachnid genus known exclusively from nine specimens from the Upper Carboniferous of Coseley, Staffordshire, United Kingdom. The genus is monotypic, represented only by the species Plesiosiro madeleyi described by Reginald Innes Pocock in his important 1911 monograph on British Carboniferous arachnids. It is the only known member of the order Haptopoda.
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.
Phalangiotarbi is an extinct arachnid order first recorded from the Early Devonian of Germany and most widespread in the Upper Carboniferous coal measures of Europe and North America. The last species are known from the early Permian Rotliegend of Germany.
Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Thelyphonida, Schizomida, Amblypygi and Araneae (spiders). It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies. Two extinct orders are also placed in this clade, Haptopoda and Uraraneida. In 2016, a newly described fossil arachnid, Idmonarachne, was also included in the Tetrapulmonata; as of March 2016 it has not been assigned to an order.
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.
Nemastomoides is an extinct genus of harvestmen known from the Carboniferous fossil record. The genus is the only member of the family Nemastomoididae and contains three described species. Nemastomoides elaveris was found in the Coal Measures of Commentry in northern France, together with Eotrogulus fayoli.
Anthracomartidae Haase, 1890 is a family of the extinct arachnid order Trigonotarbida. It is likely to be most closely related to the Archaeomartidae, based on a 2014 cladistic analysis, within the clade.
Harvestmen (Opiliones) are an order of arachnids often confused with spiders, though the two orders are not closely related. Research on harvestman phylogeny is in a state of flux. While some families are clearly monophyletic, that is share a common ancestor, others are not, and the relationships between families are often not well understood.
Eophrynus is an extinct genus of arachnids from the extinct order Trigonotarbida, which lived during the Late Carboniferous period in Europe. The genus was first described in 1871 by Henry Woodward (geologist). The name comes from Eo, meaning 'dawn', and Phrynus, an extant genus of whip spider.
Cryptomartus hindi is an extinct species of Carboniferous-aged trigonotarbid arachnid from Westphalian-aged coal strata in England and Germany.
Eophrynus prestvicii is an extinct species of arachnid belonging to the order Trigonotarbida.
Tetrophthalmi is an extinct suborder of Opiliones that had both median and lateral eyes. First described in 2014, it is known from two extinct species. Phylogenetic analysis suggests that this eye arrangement is the ancestral condition for harvestmen, placing Tetrophthalmi and Cyphophthalmi in a basal position within Opiliones.
Palaeocharinus is a genus of extinct trigonotarbid arachnids known from the Devonian of western Europe. The genus was first found and described in the Rhynie chert in the 1920s by Arthur Stanley Hirst and S. Maulik. The family to which the genus belongs may be paraphyletic.
Uraraneida is an extinct order of arachnids, known from fossils of Middle Devonian, Permian and possibly Cretaceous age. 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. In 2018, a third genus Chimerarachne, from the Cretaceous of Myanmar was proposed to belong to this group, but this placement is disputed. When the first fossils were found, they were identified as spiders, but now constitute the Uraraneida, a separate but closely related group.
Idmonarachne is an extinct genus of arachnids, containing one species, Idmonarachne brasieri. It is related to uraraneids and spiders.
