Arachnid taxonomy

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.

Dromopoda is a proposed subclass of the arachnids, including the Opiliones (harvestmen), Scorpions, Pseudoscorpions and Solifugae ("camel spiders"). The latter three are sometimes grouped as Novogenuata. This taxon was first proposed by Jeffrey Shultz in 1990 based on morphological analysis. A combined morphological and molecular analysis in 1998 supported the monophyly of Dromopoda. However, subsequent molecular and combined analyses have not supported the monophyly of Dromopoda.