Idiosoma

Idiosoma is a genus of Australian armoured trapdoor spiders that was first described by Anton Ausserer in 1871. Originally placed with the Ctenizidae, it was moved to the armoured trapdoor spiders in 1985. The name is derived from the Greek (idios), meaning "individual, unique", and (soma), meaning "body", referring to the distinctive structure of the abdomen.
Description
The skin of their abdomen 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 abdomen.
Females of the black rugose trapdoor spider (Idiosoma nigrum) can grow up to long. Males can grow up to in body length.
Behaviour
The spider digs burrows up to deep, where the temperature is relatively constant through the seasons. When prey triggers any of the trip-lines radiating from the burrow's entrance, the spider runs out of the burrow to capture ants, beetles, cockroaches, millipedes or 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 weather becomes more humid.
Species
the genus contained twenty-nine species from the states of New South Wales (NSW), South Australia (SA), Victoria (VIC) or Western Australia (WA):
Idiosoma arenaceum Rix & Harvey, 2018 – WA
Idiosoma berlandi (Rainbow, 1914) – NSW
Idiosoma castellum (Main, 1986) – WA
Idiosoma clypeatum Rix & Harvey, 2018 – WA
Idiosoma corrugatum Rix & Harvey, 2018 – SA
Idiosoma cupulifex (Main, 1957) – WA
Idiosoma dandaragan Rix & Harvey, 2018 – WA
Idiosoma formosum Rix & Harvey, 2018 – WA
Idiosoma galeosomoides Rix, Main, Raven & Harvey, 2017 – WA
Idiosoma gardneri Rix & Harvey, 2018 – WA
Idiosoma gutharuka Rix & Harvey, 2018 – WA
Idiosoma incomptum Rix & Harvey, 2018 – WA
Idiosoma intermedium Rix & Harvey, 2018 – WA
Idiosoma jarrah Rix & Harvey, 2018 – WA
Idiosoma kopejtkaorum Rix & Harvey, 2018 – WA
Idiosoma kwongan Rix & Harvey, 2018 – WA
Idiosoma manstridgei (Pocock, 1897) – WA
Idiosoma mcclementsorum Rix & Harvey, 2018 – WA
Idiosoma mcnamarai Rix & Harvey, 2018 – WA
Idiosoma montanum (Faulder, 1985) – NSW
Idiosoma nigrum Main, 1952 – WA
Idiosoma occidentale (Hogg, 1903) – WA
Idiosoma planites (Faulder, 1985) – NSW
Idiosoma rhaphiduca (Rainbow & Pulleine, 1918) – WA
Idiosoma schoknechtorum Rix & Harvey, 2018 – WA
Idiosoma sigillatum (O. Pickard-Cambridge, 1870) (type) – WA
Idiosoma smeatoni (Hogg, 1902) – SA
Idiosoma subtriste (O. Pickard-Cambridge, 1877) – SA
Idiosoma winsori (Faulder, 1985) – VIC
References
Further reading
Australian Museum Online (2003): Black Rugose Trapdoor Spider fact sheet — with picture
(1952): Notes on the genus Idiosoma, a supposedly rare Western Australian trap-door spider. W. Aust. Nat. 3: 130–137.
(1957): Biology of aganippine trapdoor spiders (Mygalomorphae: Ctenizidae). Aust. J. Zool. 5: 402–473.
(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.
Mygalomorphae genera
Spiders of Australia
Taxa named by Anton Ausserer