Idiosoma kwongan Rix & Harvey

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-western Australia, ZooKeys 756, pp. 1-121 : 51

Idiosoma kwongan Rix & Harvey sp. n. Figs 25, 272-281, 282-284, 374

Type material.

Holotype male. 10 km E. of Green Head (IBRA_GES), Western Australia, Australia, 30°04'S, 114°58'E, laterite heath, 31 August 1982, R.P. McMillan (WAM T27142).

Other material examined.

AUSTRALIA: Western Australia: 1 ♂, Eneabba, AMC Minesite, area #5 (IBRA_GES), 29°49'S, 115°16'E, hand collected, 23 November 1987, R.P. McMillan (WAM T27117DNA_Voucher_NCB_018); 1 ♂, same data (WAM T27118); 1 ♂, Mount Lesueur [Lesueur National Park] (IBRA_GES), 30°10'S, 115°12'E, 1989, K. Gaull (WAM T139468DNA_Voucher_NCB_007).

Etymology.

The specific epithet is a noun in apposition, in reference to the distribution of this species in the ‘kwongan’ Banksia heathlands of south-western Australia’s northern sandplains.

Diagnosis.

Idiosoma kwongan is one of seven highly autapomorphic species in the polyphyletic 'sigillate complex’ (Fig. 25); members of this complex can be distinguished from all other species in the nigrum-group from south-western Australia (i.e., I. formosum , I. gardneri , I. gutharuka , I. incomptum , I. intermedium , I. jarrah , I. mcclementsorum , I. mcnamarai and I. sigillatum ) by the presence of well-defined lateral sclerotic strips on the male abdomen (e.g., Figs 32, 63, 256), and by the very heavily sclerotised, leathery, ‘shield-like’ morphology of the female abdomen (e.g., Figs 1-3, 9-12, 52, 74, 96). Males of I. kwongan can be further distinguished from those of I. arenaceum by the shape of the SP4 sclerites, which are not elongate-oval (Fig. 278; cf. Fig. 63); and from I. clypeatum , I. dandaragan , I. kopejtkaorum , I. nigrum and I. schoknechtorum by the presence of semi-circular lateral indentations adjacent to the SP4 sclerites (Fig. 278, Key pane 13.1; cf. Figs 32, 85, 129, 256, 335). Males of this species can also be distinguished from those of I. corrugatum (from the Eyre Peninsula of South Australia) by the shape of the prolateral clasping spurs on tibia I, which are oriented longitudinally (Fig. 280; cf. Fig. 109). Females are unknown.

Description (male holotype).

Total length 18.1. Carapace 7.9 long, 6.0 wide. Abdomen 8.6 long, 5.5 wide. Carapace (Fig. 272) dark tan and chocolate-brown, with darker ocular region; lateral margins with uniformly-spaced fringe of porrect black setae; fovea slightly procurved. Eye group (Fig. 275) trapezoidal (anterior eye row strongly procurved), 0.7 × as long as wide, PLE–PLE/ALE–ALE ratio 2.2; ALE almost contiguous; AME separated by less than their own diameter; PME separated by 3.0 × their own diameter; PME and PLE separated by slightly more than diameter of PME, PME positioned slightly posterior to level of PLE. Maxillae and labium without cuspules. Abdomen (Figs 273, 278) irregularly oval, dark beige-brown in dorsal view with lateral sclerotic strips, dorso-lateral corrugations, and scattered dorsal sclerotic spots. Dorsal surface of abdomen (Fig. 273) more heavily setose anteriorly, with assortment of stiff, porrect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen strongly sigillate (Figs 273, 278); SP2 sclerites irregular spots; SP3 sclerites very large and circular; SP4 sclerites broadly oval, each with adjacent semi-circular lateral indentation; SP5 obscured. Legs (Figs 279-281) variable shades of dark tan, with light scopulae on tarsi I–II; distal tibia I with pair of large prolateral clasping spurs oriented longitudinally. Leg I: femur 6.6; patella 3.6; tibia 4.6; metatarsus 4.8; tarsus 3.0; total 22.5. Leg I femur–tarsus /carapace length ratio 2.8. Pedipalpal tibia (Figs 282-284) 2.2 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 282-284) setose, with field of spinules disto-dorsally. Embolus (Figs 282-284) broadly twisted and sharply tapering distally, with prominent longitudinal flange and triangular (sub-distal) embolic apophysis.

Distribution and remarks.

Idiosoma kwongan (formerly known by WAM identification code ‘MYG472’) is a poorly known species with an apparently restricted distribution in the southern Geraldton Sandplains bioregion of south-western Western Australia, from Eneabba south to Green Head and the Lesueur National Park (Fig. 374). It is closely related to the three other 'sigillate complex’ species in the northern clypeatum-clade: I. arenaceum , I. clypeatum , and I. kopejtkaorum (Fig. 25). Little is known of the biology of this species, other than that males have been collected wandering in search of females in August and November.

Conservation assessment.

Idiosoma kwongan has a known extent of occurrence of nearly 500 km2 [473 km2], although this value is likely to be a severe underestimate as it is based on only three data points, and a relatively large amount of high quality (and poorly surveyed) heathland habitat still exists throughout the southern Geraldton Sandplains. As such, we consider this species data deficient for the purposes of conservation assessment.