Mesothelae

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. Extant members of the Mesothelae 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 from the Carboniferous, over 300 million years ago.

Taxonomy

Reginald Innes Pocock in 1892 was the first to realize that the exceptional characters of the genus Liphistius (the only member of the group then known) meant that it was more different from the remaining spiders than they were among themselves. Accordingly, he proposed dividing spiders into two subgroups, Mesothelae for Liphistius, and Opisthothelae for all other spiders. The names refer to the position of the spinning organs, which are in the middle of the abdomen in Liphistius and nearer the end in all other spiders. In Greek, μέσος (mesos) means "middle", and θήλα (thēla) "teat".

Phylogeny and classification

Pocock divided his Opisthothelae into two groups, which he called Mygalomorphae and Arachnomorphae (now Araneomorphae), implicitly adopting the phylogeny shown below.

Pocock's approach was criticized by other arachnologists. Thus in 1923, Alexander Petrunkevitch rejected grouping mygalomorphs and araneomorphs into Opisthothelae, treating Liphistiomorphae (i.e. Mesothelae), Mygalomorphae and Arachnomorphae (Araneomorphae) as three separate groups. Others, such as W. S. Bristowe in 1933, put Liphistiomorphae and Mygalomorphae into one group, called Orthognatha, with Araneomorphae as Labidognatha:

In 1976, Platnick and Gertsch argued for a return to Pocock's classification, drawing on morphological evidence. Subsequent phylogenetic studies based on molecular data have vindicated this view. The accepted classification of spiders is now:

Order Araneae (spiders)

Suborder Mesothelae Pocock, 1892

Suborder Opisthothelae Pocock, 1892

Infraorder Mygalomorphae Pocock, 1892

Infraorder Araneomorphae Smith, 1902 (syn. Arachnomorphae Pocock, 1892)

Extant taxa

Initially the Mesothelae consisted of a single family, Liphistiidae. In 1923, the new genus Heptathela was described and placed in a separate tribe within Liphistiidae, Heptatheleae. In 1939, Alexander Petrunkevitch raised the tribe to a separate family, Heptathelidae. In 1985, Robert Raven reunited the two families, a view supported by Xu et al. in 2021, Breitling in 2022, and Sivayyapram et al. in 2024. Other authors have maintained two separate families. As of November 2025, the World Spider Catalog accepted the single family approach.

This produces the following internal classification of the Mesothelae:

• Family Liphistiidae
  • Subfamily Liphistiinae
    • Genus Liphistius Schiødte, 1849
  • Subfamily Heptathelinae
    • Genus Ganthela Xu & Kuntner, 2015
    • Genus Heptathela Kishida, 1923
    • Genus Luthela Xu & Li, 2022
    • Genus Qiongthela Xu & Kuntner, 2015
    • Genus Ryuthela Haupt, 1983
    • Genus Songthela Ono, 2000
    • Genus Vinathela Ono, 2000