Abstract
The aganippine shield-backed trapdoor spiders of the monophyletic nigrum-group of Idiosoma Ausserer s. l. are revised, and 15 new species are described from Western Australia and the Eyre Peninsula of South Australia: I. arenaceum Rix & Harvey, sp. n., I. corrugatum Rix & Harvey, sp. n., I. clypeatum Rix & Harvey, sp. n., I. dandaragan Rix & Harvey, sp. n., I. formosum Rix & Harvey, sp. n., I. gardneri Rix & Harvey, sp. n., I. gutharuka Rix & Harvey, sp. n., I. incomptum Rix & Harvey, sp. n., I. intermedium Rix & Harvey, sp. n., I. jarrah Rix & Harvey, sp. n., I. kopejtkaorum Rix & Harvey, sp. n., I. kwongan Rix & Harvey, sp. n., I. mcclementsorum Rix & Harvey, sp. n., I. mcnamarai Rix & Harvey, sp. n., and I. schoknechtorum Rix & Harvey, sp. n. Two previously described species from south-western Western Australia, I. nigrum Main, 1952 and I. sigillatum (O. P.-Cambridge, 1870), are re-illustrated and re-diagnosed, and complementary molecular data for 14 species and seven genes are analysed with Bayesian methods. Members of the nigrum-group are of long-standing conservation significance, and I. nigrum is the only spider in Australia to be afforded threatened species status under both State and Commonwealth legislation. Two other species, I. formosum Rix & Harvey, sp. n. and I. kopejtkaorum Rix & Harvey, sp. n., are also formally listed as Endangered under Western Australian State legislation. Here we significantly relimit I. nigrum to include only those populations from the central and central-western Wheatbelt bioregion, and further document the known diversity and conservation status of all known species.