The Mesothelae suborder currently houses only one family of spiders, members of which are still present today: Liphistiidae
Otherwise, the group includes only species that are already extinct. Mesothelae are the oldest suborder, the oldest known spider being dated back over 300 million years. The extant members of the Liphistiidae occur exclusively in Asia. The chelicerae are arranged paraxial, they have two pairs of book lungs and up to eight spinnerets. On the dorsal site of the abdomen (opisthosoma) are tergite plates.