Mesothelae
| Mesothelae Temporal range: Late Carboniferous to present |
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| A female Ryuthela secundaria | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Arachnida |
| Order: | Araneae |
| Suborder: |
Mesothelae Pocock, 1892 |
| Subdivisions | |
Mesothelae is a suborder of spiders (order Araneae) that includes a single living (extant) family, Liphistiidae, and a number of extinct families. This suborder is thought to form the sister group to all other living spiders, and retain ancestral characters, such as a segmented abdomen with spinnerets in the middle and two pairs of book lungs. Members of Liphistiidae are medium to large spiders with eight eyes grouped on a tubercle. They are only found in China, Japan, and southeast Asia.
The Heptathelidae were once considered their own family; today they are considered a subfamily of the Liphistiidae (i.e. as Heptathelinae).
Members of Mesothelae have paraxial chelicerae, two pairs of coxal glands on the legs, eight eyes grouped on a nodule, two pairs of book lungs, and no endites on the base of the pedipalp. Most have at least seven or eight spinnerets near the middle of the abdomen. Lateral spinnerets are multi-segmented.
Recent Mesothelae are characterized by the narrow sternum on the ventral side of the 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 feature, 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 mygalomorph spiders, they have two pairs of book lungs.
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