The tube-dwelling spiders (family Segestriidae) consist of two large and widespread genera (Segestria and Ariadna) and two smaller genera, Citharoceps and Gippsicola. The family is easily recognized because its members have six eyes (most spiders have eight) arranged in a semicircle and have the first three pairs of legs arranged forward (most spiders have only the first two pairs so arranged.) The leg structure appears to be an adaptation for living in silken tubes, which unlike those of the atypical tarantulas, may branch and are often built in tree bark fissures, as well as under stones. These are haplogyne primitive araneomorphs related to the Dysderidae, being placed in clade or superfamily Dysderoidea. Both Segestria and Ariadna live in North America, South America, Eurasia, Africa and New Zealand, while Ariadna also lives in Australia. This wide distribution attests to the ancient origin of this family.