Idiosoma Ausserer, 1871,

Rix, Michael G., Huey, Joel A., Cooper, Steven J. B., Austin, Andrew D. & Harvey, Mark S., 2018, Conservation systematics of the shield-backed trapdoor spiders of the nigrum-group (Mygalomorphae, Idiopidae, Idiosoma): integrative taxonomy reveals a diverse and threatened fauna from south-, ZooKeys 756, pp. 1-121: 7-16

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Idiosoma Ausserer, 1871


Genus Idiosoma Ausserer, 1871 

Idiosoma  Ausserer, 1871: 150.

Aganippe  O. P.-Cambridge, 1877: 28. Type species by subsequent designation (of Simon, 1892: 160) Aganippe subtristis  O. P.-Cambridge, 1877 (synonymised by Rix et al. 2017d: 590).

Anidiops  Pocock, 1897: 114. Type species by monotypy Anidiops manstridgei  Pocock, 1897 (synonymised by Rix et al. 2017d: 590).

Type species.

Idiops sigillatus  O. P.-Cambridge, 1870, by monotypy.


Species of Idiosoma  can be distinguished from all other Arbanitinae  by the presence of a median retrolateral digital process on the male pedipalp, distal to a burr-like RTA (this digital process secondarily reduced to a nubbin in a very few species) ( Rix et al. 2017d). Males and females of most (but not all) Idiosoma  species also possess at least one prominent pair of sclerotised sigilla on the dorsal abdomen, at position SP2 (also present in Eucanippe  ).


The genus Idiosoma  has a broad distribution across mainland Australia in all States and Territories, mostly south of the Tropic of Capricorn and west of the Great Dividing Range ( Rix et al. 2017d).

Composition and remarks.

Idiosoma  was found to be the sister-genus to Eucanippe  by Rix et al. (2017b), and includes 29 species, 15 of which are newly described in this study. A very large number of undescribed species are also known from museum collections (M. Rix, unpubl. data).

Shield-backed trapdoor spiders (the Idiosoma nigrum  -group)

Diagnosis and remarks. The monophyletic nigrum-group comprises 17 species of Idiosoma  , all but one of which are endemic to Western Australia. They can be distinguished from other congeners by the presence of a phragmotic abdominal morphology in which SP3 is uniquely sclerotised and always larger than SP2 (e.g., Figs 146, 151). Many (but not all) species possess prominent abdominal corrugations (e.g., Figs 2, 12), and the seven species in the polyphyletic 'sigillate complex’ also have a heavily sclerotised, thickened and leathery cuticle which is somewhat truncate posteriorly (Figs 1-3, 9-12), giving the abdomen a reinforced, sigillate ‘shield-like’ morphology (hence the common name). Three clades are recognised: the clypeatum-clade (four species), the intermedium-clade (three species) and the sigillatum-clade (nine species) (Fig. 25). The sole species found outside of south-western Australia, I. corrugatum  , is of uncertain affinity, due to a slightly unusual morphology and lack of sequence data.

Shield-backed trapdoor spiders are usually dark brown to black in life (Figs 1-12), and burrows are characterised by the presence of a ‘moustache-like’ arrangement of twig-lines and thin flap-type or wafer-type doors which are adorned with leaf litter debris (Figs 13-24). Most species have fairly restricted short-range endemic distributions (see Harvey 2002) which are sometimes overlapping or closely parapatric (Figs 374-377), although direct syntopy of multiple nigrum-group taxa in the field is rare.

Illustrated key to Australian shield-backed trapdoor spiders of the Idiosoma nigrum  -group

NB. While females of I. gardneri  sp. n., I. gutharuka  sp. n., I. incomptum  sp. n., and I. kwongan  sp. n. are unknown, their likely position within the key is indicated (based on male morphology and phylogeny). See Suppl. material 1 for additional images of relevant character states for males.

A By our assessment, males and females I. dandaragan  sp. n. and I. schoknechtorum  sp. n. appear to be indistinguishable morphologically; molecular data (Fig. 25) or geographic distribution (Fig. 374) are required for accurate identification.

B The unknown female of I. gardneri  sp. n. would likely key out to this couplet.

C The unknown female of I. kwongan  sp. n. would likely key out to this position.

D By our assessment, females of I. clypeatum  sp. n. and I. kopejtkaorum  sp. n. appear to be indistinguishable morphologically; males, molecular data (Fig. 25) or geographic distribution (Fig. 374) are required for accurate identification.

E The unknown females of I. gutharuka  sp. n. and I. incomptum  sp. n. would likely key out to this couplet.