Paleozoic arachnids

Pulmonoscorpius is an extinct genus of scorpion from the Mississippian Era (Early Carboniferous), discovered in Scotland. It contains a single named species, Pulmonoscorpius kirktonensis. It was one of the largest scorpions to have ever lived, with the largest known individual having an estimated length exceeding 70 cm (28 inches). Pulmonoscorpius retains several general arthropod features which are absent in modern scorpions, such as large lateral eyes and a lack of adaptations for a burrowing lifestyle. It was likely an active diurnal predator, and the presence of book lungs indicates that i

Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Uropygi (whip scorpions), Schizomida (short-tailed whip scorpions), Amblypygi (tail-less whip scorpions) 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; it has not been assigned to an order.

Phalangiotarbida 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.

Arthrolycosidae is an extinct family of arachnids, possibly spiders. Fossils placed in the family were found in the period spanning Carboniferous to Permian. 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, . 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 (those with eyes were placed in the Arthrolycosidae). Paul A. Selden has shown the fossil specimens only have "the general appearance of spiders", with segmented abdomens (opisthosomae), but no definite spinnerets.

Arthrolycosa (meaning wolf [spider] with joints) is an extinct genus of arachnids, possibly spiders, that lived about 300-250 million years ago.