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The mygalomorph spider family Nemesiidae includes 364 described species (Platnick 2013). The family has a worldwide distribution, but only five (at most) valid species occur in North America north of Mexico, all belonging in the genus Calisoga (Ubick and Ledford 2005). Of these North American species, according to Ubick and Ledford, Brachythele longitarsis and B. anomala clearly belong in the genus Calisoga but were never formally transferred to this genus. For this reason, Platnick still lists them in Brachythele and lists only three Calisoga species (C. centronetha, C. sacra, and C. theveneti—and Ubick and Ledford report that according to M.M. Bentzien in his unpublished 1976 Ph.D. thesis, "C. theveneti" are actually just very small C. longitarsis).
Nemesiids resemble tarantulas (Theraphosidae), although they are generally smaller and more slightly built; close inspection reveals that they lack the conspicuous claw tufts at the tips of their legs that are evident in theraphosids and the tips of their tarsi bear three claws instead of the two present in theraphosids.
Calisoga is known from northern and central California, with a single record from western Nevada. These spiders are found in a range of habitats, mainly oak grasslands, riparian areas, and coniferous forests, from near sea level to around 2300 m elevation, sometimes occurring even in urban areas. Calisoga live in burrows or in crevices in the ground which they line with silk and hide in as they wait for passing prey. Mature males leave their burrows to search for females and females are often flooded out of their burrows in the rainy season. Females place their egg sacs in their burrows. Calisoga sometimes enter human homes, where their large and hairy appearance, conspicuous threat display, and aggressive behavior can cause alarm, although they are not dangerous to humans. (Ubick and Ledford 2005; Bradley 2013)
In Australia, nemesiids are known as wishbone spiders because they often build forked burrows with two openings at the soil surface that would resemble a wishbone if viewed in cross section (Main 1976 cited in Bradley 2013).
Ubick and Ledford (2005) reviewed the taxonomic history of the small number of Nearctic nemesiids.