Idiosoma

Idiosoma is also the terminus for an anatomical structure of mites.

Idiosoma is a genus of trapdoor spiders in the family Idiopidae with three species, found only in Western Australia.

The genus was transferred from Ctenizidae to Idiopidae in 1985.^[1]

Idiosoma nigrum, commonly called the Black rugose trapdoor spider, can grow up to 30 mm long. Males reach a body size of up to 18 mm. The skin of their opisthosoma is hardened, with a flattened end and deep grooves running along the sides. The thickened skin helps to reduce water loss in its dry habitat. It also serves as a kind of plug to shield itself from predators. This phenomenon is called phragmosis and occurs in perfection in the spider genus Cyclocosmia (Ctenizidae). However, some parasitic wasps have evolved paper-thin abdomens and long, slender ovipositors and lay their eggs on the softer skin at the front of the spider's opisthosoma. ^[2]

Its burrow is up to 32 cm deep, where the temperature is relatively constant during the seasons. When prey trips over one of the trip-lines radiating from the burrow's entrance, the spider runs out of the burrow to capture ants, beetles, cockroaches, millipedes and moths. This is unlike many trapdoor spiders that very rarely leave their burrow. Males actively look for females, and mating takes place in the female's burrow. She lays her eggs during late spring and early summer. The spiderlings hatch in mid-summer, and stay inside the burrow until early winter, when the climate gets more humid.^[2]

Name

The genus name is derived from the Greek idios "individual, unique" and soma "body", referring to the distinctive structure of the abdomen.

Species

• Idiosoma hirsutum Main, 1952
• Idiosoma nigrum Main, 1952 — Black Rugose Trapdoor Spider
• Idiosoma sigillatum (O. P.-Cambridge, 1870)

Footnotes

References

• Australian Museum Online (2003): Black Rugose Trapdoor Spider fact sheet — with picture
• Platnick, Norman I. (2008): The world spider catalog, version 8.5. American Museum of Natural History.

Further reading

• Main, Barbara York (1952): Notes on the genus Idiosoma, a supposedly rare Western Australian trap-door spider. W. Aust. Nat. 3: 130-137.
• Main, Barbara York (1957): Biology of aganippine trapdoor spiders (Mygalomorphae: Ctenizidae). Aust. J. Zool. 5: 402-473.
• Main, Barbara York (1985): Further studies on the systematics of ctenizid trapdoor spiders: A review of the Australian genera (Araneae: Mygalomorphae: Ctenizidae). Aust. J. Zool. (suppl. Ser.) 108: 1-84.