Idiosoma incomptum 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 : 39-40

Idiosoma incomptum Rix & Harvey sp. n. Figs 25, 193-202, 203-205, 376

Type material.

Holotype male. Carnarvon, Police and Citizens Youth Centre (IBRA_CAR), Western Australia, Australia, 24°52'08"S, 113°40'59"E, outside building, morning, after rain, 10 July 2009, J.M. Waldock (WAM T99997DNA_Voucher_58).

Other material examined.

AUSTRALIA: Western Australia: 1 ♂, Boolathana Station, site BO1 (IBRA_CAR), 24°24'48"S, 113°39'47"E, wet pitfall trap, 29 May– 25 August 1995, N. Hall, WAM/CALM Carnarvon Survey (WAM T98474); 1 ♂, same data except site BO2, 24°24'47"S, 113°40'30"E, 30 May– 25 August 1995 (WAM T98469); 1 ♂, Bush Bay, site BB3 (IBRA_CAR), 25°04'40"S, 113°42'37"E, wet pitfall trap, July 1994, N. Hall, WAM/CALM Carnarvon Survey (WAM T98472); 2 ♂, Francois Peron National Park, site PE2 (IBRA_CAR), 25°52'31"S, 113°32'59"E, wet pitfall trap, 25 May– 30 August 1995, N. Hall, WAM/CALM Carnarvon Survey (WAM T98473); 1 ♂, Nanga Station, site NA2 (IBRA_CAR), 26°29'23"S, 114°03'24"E, wet pitfall trap, 11 May– 30 August 1995, N. Hall, WAM/CALM Carnarvon Survey (WAM T98470); 2 ♂, Zuytdorp, site ZU4 (IBRA_GES), 27°15'45"S, 114°09'13"E, wet pitfall trap, 18 May– 16 August 1995, N. Hall, WAM/CALM Carnarvon Survey (WAM T98475); 1 ♂, same data except site ZU5, 27°14'43"S, 114°11'36"E, 17 May– 16 August 1995 (WAM T98471).

Etymology.

The specific epithet is derived from the Latin incomptus (adjective: ‘unadorned’; see Brown 1956), in reference to the small sigilla and largely unsclerotised abdominal morphology of this species.

Diagnosis.

Idiosoma incomptum 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. incomptum 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. 199; cf. Figs 151, 173, 212, 234, 291, 313, 357), and by the absence of clearly visible SP4 sclerites (Fig. 199; cf. Figs 151, 173, 212, 234, 291, 313, 357); and from I. gutharuka by the shape of the embolus, which gradually tapers distally and is without a prominent flange (Figs 203-205; cf. Figs 190-192). 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. 201; cf. Fig. 109). Females are unknown.

Description (male holotype).

Total length 18.7. Carapace 9.3 long, 7.0 wide. Abdomen 7.6 long, 5.8 wide. Carapace (Fig. 193) dark chocolate-brown, with darker ocular region; lateral margins with uniformly-spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 196) 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 3.3 × their own diameter; PME and PLE separated by slightly more than diameter of PME, PME positioned slightly posterior to level of PLE. Maxillae with field of small cuspules confined to inner corner; labium without cuspules. Abdomen (Figs 194, 199) broadly oval, charcoal-coloured in dorsal view with faint tan mottling and assortment of stiff, porrect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen largely asigillate (Figs 194, 199); SP2 sclerites comma-shaped spots; SP3 sclerites only marginally larger than SP2 sclerites, each surrounded by pad of unsclerotised cuticle; SP4 and SP5 obscured. Legs (Figs 200-202) 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 7.9; patella 4.1; tibia 5.5; metatarsus 6.3; tarsus 3.2; total 27.0. Leg I femur–tarsus /carapace length ratio 2.9. Pedipalpal tibia (Figs 203-205) 2.5 × longer than wide; RTA burr-like, with rounded basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 203-205) setose, with field of spinules disto-dorsally. Embolus (Figs 203-205) twisted and gradually tapering distally; embolic apophysis absent.

Distribution and remarks.

Idiosoma incomptum (formerly known by WAM identification code ‘MYG130’), a member of the intermedium-clade (Fig. 25), has a relatively widespread, near-coastal distribution in Western Australia’s southern Carnarvon Basin, from Zuytdorp north to at least Boolathana Station (Fig. 376). Like I. gutharuka , I. incomptum 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. gutharuka , and the two are likely to be sister species. Little is known of the biology of I. incomptum , other than that males have been collected wandering in search of females in winter and possibly late autumn.

Conservation assessment.

Idiosoma incomptum has a known extent of occurrence of nearly 6,500 km2 [6,270 km2; with coastline as western margin excluding the Carrarang Peninsula], although this value is likely to be an underestimate (possibly severely so), due to a paucity of inland records. The area of occupancy within that range is similarly difficult to estimate based on past survey effort. As such, we consider this species data deficient for the purposes of conservation assessment.