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.
Highlights
IntroductionThe shield-backed trapdoor spiders of the genus Idiosoma Ausserer, 1871 (Figs 1–12), otherwise known as the nigrum-group (sensu Rix et al 2017b, d), are an iconic and threatened component of the Australian mygalomorph spider fauna
The shield-backed trapdoor spiders of the genus Idiosoma Ausserer, 1871 (Figs 1–12), otherwise known as the nigrum-group, are an iconic and threatened component of the Australian mygalomorph spider fauna. Renowned for their unusual morphology and biology (Main 2003), they are of long-standing conservation significance, and I. nigrum Main, 1952 (Figs 1–3, 13) remains the only spider in Australia to be afforded threatened species status under the Commonwealth’s Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act)
In Western Australia, I. nigrum is listed as Endangered under the Western Australian Wildlife Conservation Act 1950 (WAWC Act), along with two other species newly described in this paper
Summary
The shield-backed trapdoor spiders of the genus Idiosoma Ausserer, 1871 (Figs 1–12), otherwise known as the nigrum-group (sensu Rix et al 2017b, d), are an iconic and threatened component of the Australian mygalomorph spider fauna Renowned for their unusual morphology and biology (Main 2003), they are of long-standing conservation significance, and I. nigrum Main, 1952 (Figs 1–3, 13) remains the only spider in Australia to be afforded threatened species status under the Commonwealth’s Environmental Protection and Biodiversity Conservation Act 1999 (EPBC Act). Analogous to convergent morphologies in I. galeosomoides Rix, Main, Raven & Harvey, 2017 from south-western Australia, species of Galeosoma Purcell, 1903 (Idiopidae) from southern Africa, and species of Cyclocosmia Ausserer, 1871 (Ctenizidae) from North America and East Asia, these modified abdomens are able to be wedged midway down the burrow shaft upon disturbance (Fig. 3) This phragmotic behaviour presents the reinforced, sigillate abdominal ‘shield’ uppermost, presumably protecting the inhabitant from predatory attack (e.g., by wasps, ants and centipedes). All species in the nigrum-group are further endemic to the biodiversity hotspot of south-western Western Australia (see Rix et al 2015), except for a single enigmatic species from the Eyre Peninsula of South Australia, tentatively included incertae sedis within the nigrum-group
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