Idiosoma gutharuka 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 : 36-39

Idiosoma gutharuka Rix & Harvey sp. n. Figs 180-189, 190-192, 376

Type material.

Holotype male. Gutha (IBRA_AVW), Western Australia, Australia, 28°59'34"S, 115°56'23"E, wet pitfall trap, 23 May– 17 September 1996, M.S. Harvey, J.M. Waldock (WAM T38517).

Etymology.

The specific epithet is a noun in apposition derived from a contraction of ‘Gutha’ and ‘Pintharuka’, in reference to the region where this species has been found.

Diagnosis.

Idiosoma gutharuka is one of nine south-western Australian species in the intermedium- and sigillatum-clades which does not belong to the distinctive 'sigillate complex’ (Fig. 25); these nine species can be distinguished from those 'sigillate complex’ taxa (i.e., I. arenaceum , I. clypeatum , I. dandaragan , I. kopejtkaorum , I. kwongan , I. nigrum and I. schoknechtorum ) by the absence of well-defined lateral sclerotic strips on the male abdomen (e.g., Figs 151, 212, 234), and by the significantly less sclerotised morphology of the female abdomen (which may be strongly corrugate but never leathery and ‘shield-like’) (e.g., Figs 4, 7, 8, 159, 220, 242). Males of I. gutharuka can be further distinguished from those of I. formosum , I. gardneri , I. intermedium , I. jarrah , I. mcclementsorum , I. mcnamarai and I. sigillatum by the small size of the SP3 sclerites, which are only marginally larger than the SP2 sclerites (Fig. 186; cf. Figs 151, 173, 212, 234, 291, 313, 357), and by the absence of clearly visible SP4 sclerites (Fig. 186; cf. Figs 151, 173, 212, 234, 291, 313, 357); and from I. incomptum by the shape of the embolus, which is sharply tapering distally with a prominent longitudinal flange (Figs 190-192; cf. Figs 203-205). 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. 188; cf. Fig. 109). Females are unknown.

Description (male holotype).

Total length 19.4. Carapace 8.6 long, 6.6 wide. Abdomen 8.1 long, 5.6 wide. Carapace (Fig. 180) tan, with darker ocular region and partial coating of dirt on dorsal surface; lateral margins with uniformly-spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 183) trapezoidal (anterior eye row strongly procurved), 0.6 × as long as wide, PLE–PLE/ALE–ALE ratio 2.1; ALE almost contiguous; AME separated by less than their own diameter; PME separated by 4.9 × their own diameter; PME and PLE separated by slightly more than diameter of PME, PME positioned in line with level of PLE. Maxillae and labium without cuspules. Abdomen (Figs 181, 186) oval, with thin coating of dirt on dorsal surface (obscuring most of underlying cuticle) and assortment of stiff, porrect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen largely asigillate (Figs 181, 186); SP2 sclerites irregular, comma-shaped spots; SP3 sclerites only marginally larger than SP2 sclerites, each surrounded by pad of unsclerotised cuticle; SP4 and SP5 obscured. Legs (Figs 187-189) variable shades of tan, with light scopulae on tarsi I–II; distal tibia I with pair of large prolateral clasping spurs oriented longitudinally. Leg I: femur 7.8; patella 4.0; tibia 5.6; metatarsus 6.2; tarsus 3.4; total 27.0. Leg I femur–tarsus /carapace length ratio 3.1. Pedipalpal tibia (Figs 190-192) 2.4 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 190-192) setose, with field of spinules disto-dorsally. Embolus (Figs 190-192) broadly twisted and sharply tapering distally, with prominent longitudinal flange and small triangular (sub-distal) embolic apophysis.

Distribution and remarks.

Idiosoma gutharuka (formerly known by WAM identification code ‘MYG157’) is known only from Gutha, near Pintharuka in the north ern Wheatbelt bioregion of south-western Western Australia (Fig. 376). Only a single specimen has ever been collected, and nothing is known of its biology. Like I. incomptum , I. gutharuka exhibits a rudimentary, largely symplesiomorphic morphology between unmodified congeners and the more obviously phragmotic taxa in the clypeatum- and sigillatum-clades. It is most similar to I. incomptum , and the two are likely to be sister species.

Conservation assessment.

Idiosoma gutharuka is known from only a single site in the northern Wheatbelt. Given: (i) this highly restricted geographic range; (ii) the sampling effort that has occurred in surrounding areas as a result of a major biotic survey (see Keighery 2004) and a long history of incidental collecting; and (iii) the continuing decline in the area, extent and/or quality of habitat in the northern Wheatbelt agricultural zone ( Laurance et al. 2011), this species is considered Critically Endangered (B1ab[iii] + B2ab[iii]). Urgent close assessment under both Criteria A and B will be crucial to the continued survival of this species.