Idiosoma intermedium 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 : 40-43

Idiosoma intermedium Rix & Harvey sp. n. Figs 25, 206-215, 216-218, 219-227, 376

Type material.

Holotype male. Bodallin (IBRA_AVW), Western Australia, Australia, 31°22'S, 118°51'E, 26 June 1970, L.C. Birlles (WAM T139520).

Other material examined.

AUSTRALIA: Western Australia: 1 ♂, Billiburning Rock (IBRA_COO), 30°10'S, 117°55'E, 19 May 1985, B.Y. Main (WAM T139494); 1 ♀, same data (WAM T144851); ♀, same data (WAM T144854); 1 ♀, ca. 80 km NE. of Bullfinch, north of J5 (IBRA_COO), 30°18'20"S, 119°36'06"E, hand collected, 20 November 2015, M.K. Curran, D. Harms (WAM T140940DNA_Voucher_NCB_005); 1 juvenile, same data except NE. of J5, 30°15'23"S, 119°24'03"E (WAM T140939); 1 juvenile, same data except J5 deposit, 30°21'55"S, 119°36'45"E (WAM T140938); 1 ♀, Bungalbin Hill, ca. 48.2 km NNE. of Koolyanobbing (IBRA_COO), 30°29'51"S, 119°35'59"E, 9-17 October 2012, N. Dight (WAM T127934); 1 ♀, 5.5 km SE. of Koolyanobbing (IBRA_COO), 30°51'06"S, 119°33'43"E, dug from burrow, 23 August 2009, R. Teale (WAM T99749DNA_Voucher_133); 1 juvenile, Mt Manning area, site CR4 (IBRA_COO), 30°28'53"S, 119°59'43"E, open tall eucalypt woodland with mixed shrubs, 20 June 2008, J, Francesconi et al. (WAM T92079DNA_Voucher_310); 1 ♂, Mungarri Nature Reserve, south, site BE13 (IBRA_AVW), 30°20'55"S, 117°45'29"E, wet pitfall traps, 15 September 1998-25 October 1999, L. King, CALM Survey (WAM T139517DNA_Voucher_NCB_011); 1 ♂, Warrachuppin North Road, site MN2 (IBRA_AVW), 31°00'06"S, 118°41'31"E, wet pitfall traps, 21 May– 22 September 1998, N. Guthrie, CALM Survey (WAM T139519DNA_Voucher_NCB_010).

Etymology.

The specific epithet is derived from the Latin intermedius (adjective: 'in between’, ‘intermediate’; see Brown 1956), in reference to the intermediate size of the sigilla and relatively unsclerotised abdominal morphology of this species.

Diagnosis.

Idiosoma intermedium 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. intermedium can be further distinguished from those of I. gutharuka and I. incomptum by the presence of enlarged (i.e., clearly visible) SP4 sclerites (Fig. 212; 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. 213; cf. Figs 235, 292); from I. gardneri and I. sigillatum by the absence of well-defined dorso-lateral abdominal corrugations or striations (Figs 207, 212, Key pane 9.2; 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. 213; cf. Fig. 152), and by the colour of the abdomen, which is more uniformly coloured dorsally (Figs 207, 212; cf. Figs 146, 151); and from I. mcnamarai by the smaller SP4 sclerites (Fig. 212; cf. Fig. 313), and by the morphology of the SP3 sclerites, each of which may have a laterally or postero-laterally directed triangular ‘corner’ laterally (as opposed to an antero-laterally directed triangular ‘corner’) (Fig. 212, Key pane 12.3; cf. Fig. 313, Key panes 12.1, 12.2).

Females can be distinguished from those of I. mcclementsorum and I. sigillatum by the absence of reinforced, sclerotised ridges on the abdomen (Figs 220, 223; cf. Figs 299, 302, 365, 368); from I. formosum and I. mcnamarai by the size of the SP4 sclerites, which are not significantly larger than the SP2 sclerites (Fig. 223; cf. Figs 162, 324); and from I. jarrah by the slightly larger size of the SP3 and SP4 sclerites (Fig. 223; cf. Fig. 245) [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. 214; cf. Fig. 109), and by the shape of the female eye group, which is broadly trapezoidal (Fig. 222; cf. Fig. 117).

Description (male holotype).

Total length 19.8. Carapace 9.7 long, 7.3 wide. Abdomen 8.2 long, 5.4 wide. Carapace (Fig. 206) dark tan, with darker ocular region; lateral margins with uniformly-spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 209) trapezoidal (anterior eye row strongly procurved), 0.6 × as long as wide, PLE–PLE/ALE–ALE ratio 2.3; ALE almost contiguous; AME separated by less than their own diameter; PME separated by 5.3 × their own diameter; PME and PLE separated by slightly more than diameter of PME, PME positioned in line with level of PLE. Maxillae with field of small cuspules confined to inner corner; labium without cuspules. Abdomen (Figs 207, 212) oval, charcoal-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 207, 212); SP2 sclerites comma-shaped spots; SP3 sclerites circular with irregular margins, each with unsclerotised triangular ‘corner’ laterally; SP4 sclerites oval, each surrounded by chevron-like pad of unsclerotised cuticle laterally; SP5 obscured. Legs (Figs 213-215) 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 8.0; patella 4.1; tibia 5.7; metatarsus 6.1; tarsus 3.7; total 27.5. Leg I femur–tarsus /carapace length ratio 2.8. Pedipalpal tibia (Figs 216-218) 2.4 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 216-218) setose, with field of spinules disto-dorsally. Embolus (Figs 216-218) broadly twisted and sharply tapering distally, with prominent longitudinal flange and triangular (sub-distal) embolic apophysis.

Description (female WAM T99749).

Total length 25.0. Carapace 10.5 long, 7.3 wide. Abdomen 11.6 long, 8.9 wide. Carapace (Fig. 219) dark tan, with darker ocular region; fovea procurved. Eye group (Fig. 222) trapezoidal (anterior eye row strongly procurved), 0.6 × as long as wide, PLE–PLE/ALE–ALE ratio 2.4; ALE almost contiguous; AME separated by approximately their own diameter; PME separated by 1.9 × 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. 224); labium without cuspules. Abdomen (Figs 220, 223) broadly oval, dark grey-brown in dorsal view with tan mottling. Posterior abdomen moderately sigillate (Figs 220, 223); SP2 sclerites irregular, comma-shaped 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. Legs (Figs 225-226) variable shades of dark tan; scopulae present on tarsi and metatarsi I–II; tibia I with one stout pro-distal macroseta (broken at base) and row of seven longer retroventral macrosetae; metatarsus I with nine stout macrosetae; tarsus I with distal cluster of short macrosetae. Leg I: femur 6.4; patella 4.2; tibia 4.1; metatarsus 3.0; tarsus 2.4; total 20.1. Leg I femur–tarsus /carapace length ratio 1.9. Pedipalp dark tan, spinose on tibia and tarsus, with thick tarsal scopula. Genitalia (Fig. 227) with pair of short spermathecae on broad ‘stems’, each bearing dense field of glandular vesicles distally, and more sparsely distributed glandular field sub-distally.

Distribution and remarks.

Idiosoma intermedium (formerly known by WAM identification code ‘MYG475’), the nominate member of the intermedium-clade (Fig. 25), has a relatively widespread albeit poorly defined distribution in the eastern Wheatbelt and north-western Coolgardie bioregions of south-western Western Australia (Fig. 376). Its known range extends from Bodallin north to Billiburning Rock in the eastern Wheatbelt, and east to near the Helena-Aurora Range, Mount Manning, and Koolyanobbing in the Coolgardie bioregion. Like I. jarrah , I. formosum and I. mcnamarai , I. intermedium exhibits a transitional morphology between other species in the intermedium-clade (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 late autumn and winter.

Conservation assessment.

In 2017, Idiosoma intermedium was formally assessed as 'priority 3' fauna; this assessment incorporated the latest taxonomic, geographic and genetic data summarised in the current study (with a number of additional records also identified subsequently). It has a known extent of occurrence of nearly 14,500 km2 [14,102 km2] (a likely underestimate due to limited survey effort), and while it therefore cannot be considered threatened under Criterion B, a 'priority 3' recommendation was made due to the occurrence of this species in areas prospective for mining and mineral resources. Further close assessment under both Criteria A and B is warranted in the future.