Idiosoma schoknechtorum 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 : 57-61

Idiosoma schoknechtorum Rix & Harvey sp. n. Figs 10, 25, 18, 329-338, 339-341, 342-350, 374

Idiosoma ‘nigrum’ Main, 1952: 135 (in part; cited specimens from Mount Dick and Northam). Main 1957b: 440 (in part; cited specimens from Beverley, Connolly Gully, Flint Gully, Jimperding Hill, Mount Dick, Northam, Quairading, Toodyay and E. of York).

Type material.

Holotype male. Beverley (IBRA_AVW), Western Australia, Australia, 32°06'S, 116°55'E, May 1954, H.W. Norris (WAM T139512).

Other material examined.

AUSTRALIA: Western Australia: 1 ♀, Bakers Hill (IBRA_JAF), 31°45'S, 116°27'E, 1 October 1966, G.H. Lowe (WAM T27116); 1 ♀, 'Connolly Gully’, 26 miles NW. of Brookton, 38 miles S. of Karragullen turnoff on Kelmscott-Brookton Road (IBRA_JAF), 32°20'S, 116°38'E, 18 May 1955, B.Y. Main (WAM T144801); 1 juvenile, Cunaring Hill, 2 miles off Brookton-Kelmscott Road on track S. to Williams (IBRA_AVW), 32°25'S, 116°48'E, 5 March 1959, B.Y. Main (WAM T144841); 1 ♀, Jimperding Hill, Avon Valley (IBRA_JAF), 31°35'S, 116°20'E, 17 November 1952, B.Y. Main (WAM T144776); 1 ♀, same data (WAM T144777); 1 ♀, same data (WAM T144778); 1 juvenile, 32 miles S. of Karragullen turnoff on Kelmscott-Brookton Road (IBRA_JAF), 32°16'S, 116°24'E, 18 May 1955, B.Y. Main (WAM T144800); 1 ♂, Meckering (IBRA_AVW), 31°37'S, 117°00'E, 11 May 1963, H.E. Lamont (WAM T27121); 1 ♀, Meenaar Nature Reserve, 9 km E. of Grass Valley, off Great Eastern Highway (IBRA_AVW), 31°38'19"S, 116°53'41"E, hand collected, under mallee in woodland, 15 July 2014, M.G. Rix, M.S. Harvey (WAM T133465DNA_Voucher_154); 1 ♀, 105 Mile Peg, Quairading Road, E. of Perth (IBRA_AVW), 32°01'S, 117°26'E, 14 January 1954, M. Littlejohn (WAM T144782); 1 ♀, Mount Dick (via Northam) (IBRA_AVW), 31°35'S, 116°42'E, 17 June 1952, B.Y. Main (WAM T144763); 1 juvenile, same data (WAM T144803); 1 ♀, same data (WAM T144804); 1 ♀, Northam (IBRA_AVW), 31°39'S, 116°40'E, 5 June 1974, D. Martin (WAM T27122); 1 ♀, same locality data, June 1952, C.G. Jessup (WAM T144772); 1 juvenile, Red Hill Road, near Jimperding, several miles W. of Toodyay (IBRA_JAF), 31°35'S, 116°20'E, 21 June 1952, B.Y. Main (WAM T144771); 1 juvenile, about 6 miles W. of Toodyay on Red Hill Road (IBRA_AVW), 31°37'S, 116°24'E, 17 November 1952, B.Y. Main (WAM T144774); 1 juvenile, same data (WAM T144775); 1 juvenile, same data (WAM T144809); 1 ♂, Westdale, S. side of road (IBRA_JAF), 32°19'S, 116°37'E, pitfall trap, 20 July 1969, B.Y. Main (WAM T139513); 1 ♀, Wongamine Nature Reserve (IBRA_AVW), 31°29'S, 116°34'E, September 1990, B.Y. Main (WAM T144845); 1 ♀, York (IBRA_AVW), 31°53'S, 116°46'E, 3 May 1971, P.A. Cray (WAM T27124); 1 ♀, same data except 1 January 1974, N. Giles (WAM T27125); 1 ♀, 4.2 km SW. of York (IBRA_AVW), 31°55'03"S, 116°44'30"E, dug from burrow, 17 May 2016, D. Schoknecht (WAM T140765DNA_Voucher_NCB_004); 1 juvenile, 18 miles E. of York (IBRA_AVW), 31°52'S, 117°06'E, 6 March 1955, B.Y. Main (WAM T144826).

Etymology.

The specific epithet is named in honour of Daniel and Noel Schoknecht, for collecting an important (and sequenceable) female specimen of this species on their property SW. of York.

Diagnosis.

Idiosoma schoknechtorum 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. schoknechtorum can be further distinguished from those of I. arenaceum by the shape of the SP4 sclerites, which are not elongate-oval (Fig. 335; cf. Fig. 63); from I. kwongan by the absence of semi-circular lateral indentations adjacent to the SP4 sclerites (Fig. 335; cf. Fig. 278, Key pane 13.1); from I. clypeatum and I. kopejtkaorum by the presence of a prominent sub-distal embolic apophysis (Key pane 14.1; cf. Key panes 14.2, 14.3); and from I. nigrum by the more heavily setose morphology of the dorsal abdomen (Fig. 330; cf. Fig. 27), and by the shape of the SP4 sclerites, which are circular or oval (Fig. 335; cf. Fig. 32). By our assessment, males of I. schoknechtorum are morphologically indistinguishable from those of I. dandaragan ; molecular data (Fig. 25) or geographic distribution (Fig. 374) are required for accurate identification.

Females can be distinguished from those of I. arenaceum by the shape of the SP4 sclerites, which are not elongate-oval (Fig. 343, Key pane 23.3; cf. Fig. 74, Key pane 21.1); from I. clypeatum and I. kopejtkaorum by the size of the SP4 sclerites, which are greater than half the size of the SP3 sclerites (Fig. 343, Key pane 23.3; cf. Figs 96, 267, Key panes 22.1, 22.2); and from I. nigrum by the shape of the SP4 sclerites, which are circular or broadly oval (Fig. 343, Key pane 23.3; cf. Figs 43, 52, Key pane 23.1), and by the presence of well-defined SP5 sclerites (Fig. 343, Key pane 23.3; cf. Figs 43, 52, Key pane 23.1) [NB. females of I. kwongan are unknown]. By our assessment, females of I. schoknechtorum are morphologically indistinguishable from those of I. dandaragan ; molecular data (Fig. 25) or geographic distribution (Fig. 374) are required for accurate identification.

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. 337; cf. Fig. 109), and by the shape of the female eye group, which is broadly trapezoidal (Fig. 345; cf. Fig. 117).

Description (male holotype).

Total length 20.6. Carapace 8.6 long, 6.4 wide. Abdomen 9.3 long, 6.7 wide. Carapace (Fig. 329) tan, with darker ocular region; lateral margins with uniformly spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 332) trapezoidal (anterior eye row strongly procurved), 0.7 × 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 3.7 × 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 330, 335) broadly oval, beige-brown in dorsal view with lateral sclerotic strips, dorso-lateral corrugations, and scattered dorsal sclerotic spots. Dorsal surface of abdomen (Fig. 330) more heavily setose anteriorly, with assortment of stiff, porrect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen strongly sigillate (Figs 330, 335); SP2 sclerites irregular, comma-shaped spots; SP3 sclerites very large and circular; SP4 sclerites broadly oval; SP5 obscured. Legs (Figs 336-338) 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 7.7; patella 3.9; tibia 5.2; metatarsus 5.5; tarsus 3.4; total 25.6. Leg I femur–tarsus /carapace length ratio 3.0. Pedipalpal tibia (Figs 339-341) 2.3 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 339-341) setose, with field of spinules disto-dorsally. Embolus (Figs 339-341) broadly twisted and sharply tapering distally, with prominent longitudinal flange and triangular (sub-distal) embolic apophysis.

Description (female WAM T140765).

Total length 25.8. Carapace 10.4 long, 7.5 wide. Abdomen 12.2 long, 12.1 wide. Carapace (Fig. 342) dark tan, with darker ocular region; fovea procurved. Eye group (Fig. 345) 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 2.75 × 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. 347); labium without cuspules. Abdomen (Figs 343, 346) dark brown-black, corrugate and highly sclerotised, with leathery appearance typical of those species in the 'sigillate complex’ (see Fig. 25). Posterior face of abdomen (Fig. 346, Key pane 23.3) with truncate ‘shield-like’ morphology; SP3 sclerites very large and circular; SP4 sclerites broadly oval; SP5 sclerites small and oval. Legs (Figs 348-349) variable shades of dark 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 6.3; patella 4.0; tibia 3.9; metatarsus 3.1; tarsus 2.3; total 19.6. Leg I femur–tarsus /carapace length ratio 1.9. Pedipalp dark tan, spinose on tibia and tarsus, with thick tarsal scopula. Genitalia (Fig. 350) with pair of short, subtriangular spermathecae, each bearing dense field of glandular vesicles distally, and more sparsely distributed glandular field sub-distally.

Distribution and remarks.

Idiosoma schoknechtorum (formerly known by WAM identification code ‘MYG518’) (Fig. 10), a 'sigillate complex’ member of the diverse sigillatum-clade (Fig. 25), is a recently recognised species with a restricted distribution in the central-western Wheatbelt and north-eastern Jarrah Forest bioregion of south-western Western Australia (east of Perth) (Fig. 374). Long confused with its closely related sister species I. nigrum , the range of I. schoknechtorum extends from near Toodyay, the Wongamine Nature Reserve and Meckering in the north, south to near Jarrahdale and Westdale, and east to near Quairading. Within this range it is the only species with a highly sigillate (sclerotised) abdominal morphology, although the distribution of I. nigrum closely approaches that of I. schoknechtorum north of Meckering and Wongamine.

This species is very similar to I. nigrum and I. dandaragan in most respects, and burrows are adorned with a typical ‘moustache-like’ arrangement of twig-lines (Fig. 18). At some localities (e.g., Grass Valley) it may be locally common, although little is known of its biology, and surprisingly few specimens have been collected despite its proximity to Perth. Males have been collected wandering in search of females in May and July.

Conservation assessment.

Idiosoma schoknechtorum has a known extent of occurrence (EOO) of nearly 5,500 km2 [5,296 km2]. The area of occupancy within that range is difficult to estimate given the distributional division between the Jarrah Forest bioregion and the more heavily cleared Wheatbelt bioregion, but is certainly less than 2,000 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) and a long history of incidental collecting; (iii) the occurrence of the species at a number of severely fragmented sites; and (iv) the continuing decline in the area, extent and/or quality of habitat in the western Wheatbelt agricultural zone ( Laurance et al. 2011), this species is considered Vulnerable (B1ab[iii] + B2ab[iii]). Further close assessment under both Criteria A and B is warranted in the future.