Tetrapulmonata

Tetrapulmonata is a non-ranked supra-ordinal group of arachnids. It is composed of Thelyphonida, Schizomida, Amblypygi and Araneae. It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies.

Etymology

It receives its name from the presence of paired book lungs occupying the second and third opisthosomal segments, although the posterior pair is absent in Schizomida. Previous synonyms of this lineage are rejected; "Caulogastra Pocock, 1893" refers to pedicel, which is symplesiomorphic for the lineage and convergent with Solifugae, and "Arachnidea Van der Hammen, 1977" is easily confused with Arachnida. The clade is referred to as Pantetrapulmonata when the extinct trigonotarbid arachnids are included.

The name "Pulmonata" has been used for this group as recently as 2000, in the first paragraph of an article in Journal of Paleontology, but this creates an ambiguity because Pulmonata is a group of gastropods.

Types

Other synapomorphies of Tetrapulmonata include a large postcerebral pharynx (reduced in Uropygi), prossomal endosternite with four segmental components, subchelate chelicerae, a complex coxotrochanteral joint in the walking legs, a pretarsal depressor muscle arising in the patella (convergent with Dromopoda, lost in Amblypygi), a pedicel formed, in part, by ventral elements of the second opisthomal segment and a spermatozoon axoneme a 9+3 microtubule arrangement.