Idiosoma mcnamarai 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 : 55-57

Idiosoma mcnamarai Rix & Harvey sp. n. Figs 25, 307-316, 317-319, 320-328, 375

Type material.

Holotype male. Trayning (IBRA_AVW), Western Australia, Australia, 31°06'S, 117°47'E, 1 July 1992, A. Dugand (WAM T26107DNA_Voucher_NCB_009).

Other material examined.

AUSTRALIA: Western Australia: 1 ♂, Bruce Rock-Doodlakine Road, site KL4 (IBRA_AVW), 31°51'26"S, 118°06'14"E, wet pitfall traps, 30 October 1997-22 May 1998, P. Van Heurck, N. Guthrie, CALM Survey (WAM T139518DNA_Voucher_NCB_008); 1 ♀, 7 km. N. of Cleary (IBRA_AVW), 30°22'S, 117°39'E, 22 July 1983, B.Y. Main (WAM T139496DNA_Voucher_NCB_014); 1 ♀, same data except at water catchment, 16 July 1984 (WAM T144848); 1 ♀, same data (WAM T144849); 1 ♀, same data (WAM T144850); 1 ♀, 30.7 km N. of Cleary on Paynes Find Road (IBRA_AVW), 30°10'S, 117°42'E, 23 July 1983, B.Y. Main (WAM T144846); 1 ♀, same data (WAM T144847); 1 ♀, Dajoing Rock (IBRA_AVW), 30°26'S, 118°04'E, 17 March 1985, B.Y. Main (WAM T144853); 1 ♂, East Yorkrakine Nature Reserve, site EYRJ1 (IBRA_AVW), 31°23'S, 117°40'E, wet pitfall traps, 24 July– 3 August 1989, G. Friend et al. (WAM T44169).

Etymology.

The specific epithet is a named in honour of the late Keiran McNamara (1954-2013), in recognition of his considerable efforts in securing critical funding for the Salinity Action Plan Survey (later 'State Salinity Strategy’) of the Western Australian agricultural zone (run by the then Department of Conservation and Land Management from 1997-2000), which resulted in the collection of this and numerous other species of Idiosoma .

Diagnosis.

Idiosoma mcnamarai 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. mcnamarai can be further distinguished from those of I. gutharuka and I. incomptum by the presence of enlarged (i.e., clearly visible) SP4 sclerites (Fig. 313; cf. Figs 186, 199); from I. jarrah and I. mcclementsorum by the colour of the legs, which do not have strongly contrasting bright yellow or orange-yellow femora (Fig. 314; cf. Figs 235, 292); from I. gardneri and I. sigillatum by the absence of well-defined dorso-lateral abdominal corrugations or striations (Figs 308, 313; cf. Figs 168, 173, 352, 357, Key pane 9.1); from I. formosum by the shape of tibia I, which is longer (with the prolateral clasping spurs occupying the distal third of the segment) (Fig. 314; cf. Fig. 152), and by the colour of the abdomen, which is more uniformly coloured dorsally (Figs 308, 313; cf. Figs 146, 151); and from I. intermedium by the larger SP4 sclerites (Fig. 313; cf. Fig. 212), and by the morphology of the SP3 sclerites, each of which have an anteriorly directed triangular corner laterally (as opposed to a laterally or postero-laterally directed triangular corner) (Fig. 313, Key panes 12.1, 12.2; cf. Fig. 212, Key pane 12.3)

Females can be distinguished from those of I. mcclementsorum and I. sigillatum by the absence of reinforced, sclerotised ridges on the abdomen (Figs 321, 324; cf. Figs 299, 302, 365, 368); from I. intermedium and I. jarrah by the size of the SP4 sclerites, which are significantly larger than the SP2 sclerites (Fig. 324; cf. Figs 223, 245); and from I. formosum by the colour of the abdomen, which is more uniformly coloured dorsally (Figs 321, 324; cf. Figs 159, 162) [NB. females of I. gardneri , I. gutharuka and I. incomptum are unknown].

This species can also be distinguished from I. corrugatum (from the Eyre Peninsula of South Australia) by the shape of the prolateral clasping spurs on the male tibia I, which are oriented longitudinally (Fig. 315; cf. Fig. 109), and by the shape of the female eye group, which is broadly trapezoidal (Fig. 323; cf. Fig. 117).

Description (male holotype).

Total length 18.4. Carapace 8.3 long, 6.0 wide. Abdomen 7.2 long, 4.1 wide. Carapace (Fig. 307) tan, with darker ocular region; lateral margins with uniformly spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 310) 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 3.3 × 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 308, 313) irregularly oval, grey-brown in dorsal view with tan mottling and assortment of stiff, porrect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen moderately sigillate (Figs 308, 313); SP2 sclerites irregular spots; SP3 sclerites circular, each with unsclerotised, anteriorly directed triangular ‘corner’ laterally; SP4 sclerites broadly oval, each surrounded by chevron-like pad of unsclerotised cuticle laterally; SP5 obscured. Legs (Figs 314-316) 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 7.2; patella 3.5; tibia 5.0; metatarsus 5.2; tarsus 3.2; total 24.1. Leg I femur–tarsus /carapace length ratio 2.9. Pedipalpal tibia (Figs 317-319) 2.5 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 317-319) setose, with field of spinules disto-dorsally. Embolus (Figs 317-319) broadly twisted and sharply tapering distally, with prominent longitudinal flange and triangular (sub-distal) embolic apophysis.

Description (female WAM T139496).

Total length 26.0. Carapace 10.8 long, 7.4 wide. Abdomen 10.6 long, 10.9 wide. Carapace (Fig. 320) tan, with darker ocular region; fovea procurved. Eye group (Fig. 323) trapezoidal (anterior eye row strongly procurved), 0.6 × as long as wide, PLE–PLE/ALE–ALE ratio 3.0; ALE almost contiguous; AME separated by approximately their own diameter; PME separated by 4.7 × their own diameter; PME and PLE separated by more than diameter of PME, PME positioned in line with level of PLE. Maxillae with field of cuspules confined to inner corner (Fig. 325); labium without cuspules. Abdomen (Figs 321, 324) broadly oval and somewhat truncate posteriorly, beige-brown in dorsal view, with numerous stout setae on sclerotic bases and scattered sclerotic spots; longest stout setae clustered along median cardiac region. Posterior abdomen moderately sigillate (Figs 321, 324); SP2 sclerites irregular spots; SP3 sclerites subcircular with irregular margins, each surrounded by pad of unsclerotised cuticle; SP4 sclerites subcircular with irregular margins, each surrounded by chevron-like pad of unsclerotised cuticle laterally; SP5 obscured; posterior margin of abdomen weakly corrugate, with rows of modified stout setae. Legs (Figs 326-327) variable shades of tan; scopulae present on tarsi and metatarsi I–II; tibia I with one stout pro-distal macroseta and row of five longer retroventral macrosetae; metatarsus I with eight stout macrosetae; tarsus I with distal cluster of short macrosetae. Leg I: femur 6.7; patella 4.2; tibia 4.0; metatarsus 3.2; tarsus 2.4; total 20.5. Leg I femur–tarsus /carapace length ratio 1.9. Pedipalp tan, spinose on tibia and tarsus, with thick tarsal scopula. Genitalia (Fig. 328) with pair of obliquely angled spermathecae, each bearing dense field of glandular vesicles distally, and more sparsely distributed glandular field sub-distally.

Distribution and remarks.

Idiosoma mcnamarai (formerly known by WAM identification code ‘MYG520’), a member of the diverse sigillatum-clade (Fig. 25), is a rare species with a restricted distribution in the central-eastern Wheatbelt bioregion of south-western Western Australia, from Bruce Rock north to Lake Moore (Fig. 375). Its range follows a thin longitudinal band, likely associated with substrate and rainfall characteristics just west of the red soil transition. North of Cleary, this distribution overlaps the southern extent of the range of its closely related sister species I. formosum , and in the Durokoppin/East Yorkrakine region it overlaps with I. nigrum . Like I. formosum , I. intermedium , and I. jarrah , I. mcnamarai exhibits a transitional morphology between largely unmodified species in the intermedium-lineage’ (i.e. I. incomptum and I. gutharuka ), and the more obviously phragmotic taxa in the clypeatum- and sigillatum-clades. Little is known of the biology of this species, other than that males have been collected wandering in search of females in winter.

Conservation assessment.

Idiosoma mcnamarai has a known extent of occurrence of nearly 6,000 km2 [5,862 km2], and an area of occupancy within that range of <500 km2. Given: (i) this geographic range; (ii) the sampling effort that has occurred in surrounding areas as a result of a major biotic survey (see Keighery 2004); (iii) the occurrence of the species at <10 severely fragmented sites; and (iv) the continuing decline in the area, extent and/or quality of habitat in the central-eastern Wheatbelt agricultural zone ( Laurance et al. 2011), this species is considered Endangered (B1ab[iii] + B2ab[iii]). Further close assessment under both Criteria A and B will be crucial to the continued survival of this species.