In addition to accounting for over 90% of spider species

The only living members of the primitive Mesothelae are the family Liphistiidae, found only in Southeast Asia, China, and Japan.[69] Most of the Liphistiidae construct silk-lined burrows with thin trapdoors, although some species of the genus Liphistius build camouflaged silk tubes with a second trapdoor as an emergency exit. Members of the genus Liphistius run silk "tripwires" outwards from their tunnels to help them detect approaching prey, while those of genus Heptathela do not and instead rely on their built-in vibration sensors.[72] Spiders of the genus Heptathela have no venom glands although they do have venom gland outlets on the fang tip.[73]

The extinct families Arthrolycosidae, found in Carboniferous and Permian rocks, and Arthromygalidae, so far found only in Carboniferous rocks, have been classified as members of the Mesothelae
The Mygalomorphae, which first appeared in the Triassic period,[62] are generally heavily built and hairy, with large, robust chelicerae and fangs.[69] Well-known examples include tarantulas, trapdoor spiders and the Australasian funnel-web spiders.[8] Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "balloon" by using air currents for transport, their populations often form clumps.[69] In addition to arthropods, mygalomorphs prey on frogs and lizards, and snails
In addition to accounting for over 90% of spider species, the Araneomorphae, also known as the "true spiders", include orb-web spiders, the cursorial wolf spiders, and jumping spiders,[69] as well as the only known herbivorous spider, Bagheera kiplingi.[32] They are distinguished by having fangs that oppose each other and cross in a pinching action, in contrast to the Mygalomorphae, which have fangs that are nearly parallel in alignment