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The Mesothelae are a suborder of (order Araneae). The division of extant members of the suborder into families has varied. A single extant family Liphistiidae may be accepted, with two subfamilies: Liphistiinae, containing only the genus Liphistius, and Heptathelinae, with seven genera. Alternatively, the two subfamilies may be treated as separate families, Liphistiidae and Heptathelidae. , the World Spider Catalog accepted the single family approach. There are also a number of extinct families.
This suborder is thought to form the sister group to all other living spiders, and to retain ancestral characters, such as a segmented opisthosoma with spinnerets in the middle and two pairs of . Extant members of the Mesothelae are medium to large spiders with eight Spider vision 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.
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)
This produces the following internal classification of the Mesothelae:
Recent Mesothelae are characterized by the narrow sternum on the ventral side of the cephalothorax (prosoma). Several plesiomorphic characteristics may be useful in recognizing these spiders: there are tergite plates on the dorsal side and the almost median position of the spinnerets on the ventral side of the opisthosoma. Although it has been claimed that they lack venom glands and ducts, which almost all other spiders have, subsequent works have demonstrated that at least some, possibly all, do in fact have both the glands and ducts. All Mesothelae have eight spinnerets in four pairs. Like Mygalomorphae, they have two pairs of .
Species of Liphistius have 'fishing lines' in front of the entrances to the burrows that they construct, unlike members of the subfamily Heptathelinae. They also have a paired Spermatheca (unpaired in Heptathelinae), and have a conductor in their palpal bulb. Their long palps can confusingly look like an extra pair of legs, a mistake also made of some Solifugae.
Between 2015 and 2019 six genera of Mesothele spider in four families were described from Late Cretaceous (Cenomanian) aged Burmese amber in Myanmar. Cretaceothele (Cretaceothelidae) Burmathele (Burmathelidae), Parvithele, Pulvillothele (Parvithelidae) Intermesothele and Eomesothele (Eomesothelidae)
J. Wunderlich. 2017. New and rare fossil spiders (Araneae) in mid Cretaceous amber from Myanmar (Burma), including the description of new extinct families of the suborders Mesothelae and Opisthothelae, as well as notes on the taxonomy, the evolution and the biogeography of the Mesothelae. ''Ten Papers on Fossil and Extant Spiders (Araneae). Beiträge zur Araneologie'' '''10''':72-279
(2026). 9781869778507, Magnolia Press. ISBN 9781869778507
J. Wunderlich. 2015. On the evolution and the classification of spiders, the Mesozoic spider faunas, and descriptions of new Cretaceous taxa mainly in amber from Myanmar (Burma) (Arachnida: Araneae). ''Mesozoic Spiders (Araneae): Ancient Spider Faunas and Spider Evolution, Beiträge zur Araneologie'' '''9''':21-408
J. Wunderlich. 2019. What is a spider?. ''Beiträge zur Araneologie'' '''12''':1-32
J. Haupt (2026). 9783510550418, Schweizerbart & Borntraeger Science Publishers. . ISBN 9783510550418
(1999). 9787537518925, Hebei University of Science and Technology Publishing House. ISBN 9787537518925
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