Liphistiidae

The spider family Liphistiidae was first recognized by Tamerlan Thorell in 1869. When narrowly circumscribed, it comprises a single genus Liphistius, native to Southeast Asia;, this was the circumscription accepted by the World Spider Catalog. The family contains the most basal living spiders, belonging to the suborder Mesothelae. The family has also been circumscribed more broadly to include the family Heptathelidae as a subfamily, Heptathelinae, with the narrowly circumscribed Liphistiidae becoming the subfamily Liphistiinae.

Taxonomy
The family Liphistiidae was erected by Tamerlan Thorell in 1869 for the genus Liphistius. Initially, it was the only family placed in the suborder Mesothelae. In 1923, Kyukichi Kishida described a new genus, Heptathela, and suggested creating two tribes within the Liphistiidae corresponding to the genera Liphistius and Heptathela. In 1939, Alexander Petrunkevitch raised the tribe Heptatheleae to a separate family, Heptathelidae, thus restoring the narrower circumscription of the Liphistiidae. In 1985, Robert Raven reunited the two families, a view supported by Breitling in 2022. Other authors have maintained two separate families, a position accepted by the World Spider Catalog.

Liphistius, the sole genus in the narrowly circumscribed family Liphistiidae, is found mainly in Southeast Asia (Laos, Myanmar, Thailand, Malaysia and Sumatra), with a few species found in China. The Heptathelidae are found further north: five genera in northern Vietnam and China and two genera in Japan and offshore islands (Okinawa, Ryukyu Islands).

Phylogeny
Molecular phylogenetic studies have repeatedly shown that the suborder Mesothelae is monophyletic, at least as regards extant (living) species, with the two families forming separate clades:

Genera
, the World Spider Catalog accepted the narrow circumscription of the family Liphistiidae, in which it contains only one genus:
 * Liphistius Schiödte, 1849 — Asia

Description
Members of the Liphistiidae share features with the other Mesothelae family, Heptathelidae. They are medium to large spiders. They have downward pointing, daggerlike chelicerae. Like other members of the suborder Mesothelae, and unlike all other extant spiders, they have a segmented series of plates (tergites) on the upper surface of all segments of the abdomen and their spinnerets are placed in the middle of the underside of the abdomen, rather than at the end. Their sternum (a plate on the underside of the cephalothorax) is narrow, and there is another smaller ventral plate (the sternite) between the fourth pair of legs. The carapace is mostly flat, though it can be slightly elevated near the head. The eyes are distinctly clustered together on a single nodule. The anterior median eyes are small, but the posterior median eyes are large and round. The lateral eyes are long and kidney-shaped. The distal leg segments have strong spines and three claws. The respiratory system consists only of book lungs, which could help explain why they are relatively inactive. Unlike heptathelids, the male palp has a tibial apophysis.

In the past, they were frequently believed to lack venom, but in 2010 it was shown that at least some Liphistius species have venom glands.

Liphistiids are tube-dwelling spiders that construct rudimentary trap-doors. They spend most of their time in their tubes and are rarely seen above ground. They are active at night and live for many years. Unlike members of the family Heptathelidae, Liphistiidae spiders construct signal lines radiating from the entrance to their burrows. Adult males sometimes wander in search for females, but females rarely leave their burrows.



Fossil record
While some Carboniferous fossil spiders have been assigned to Mesothelae, the only fossil to be explicitly placed in the family Liphistiidae is Cretaceothele lata Wunderlich, 2015 from the Cretaceous Burmese amber of Myanmar. The fossil genus was diagnosed as having an eye-field wider than that in living species. It was later placed in its own, monotypic family Cretaceothelidae.