Idiosoma dandaragan 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 : 30-31

Idiosoma dandaragan Rix & Harvey sp. n. Figs 25, 123-132, 133-135, 136-144, 374

Idiosoma ‘nigrum’ Main, 1957b: 440 (in part; cited specimens from S. of Moora and E. of Watheroo).

Type material.

Holotype male. 12.2 miles S. of Moora on Mogumber Road (IBRA_JAF), Western Australia, Australia, 30°49'S, 116°02'E, 25 May 1954, B.Y. Main (WAM T139522).

Paratypes. 1 ♂, same data as holotype (WAM T139523); 1 ♂, same data (WAM T139525); 1 ♂, same data (WAM T139526).

Other material examined.

AUSTRALIA: Western Australia: 1 ♂, 5.6 miles S. of Moora on Mogumber Road (IBRA_AVW), 30°43'S, 116°01'E, 25 May 1954, B.Y. Main (WAM T139524); 1 ♂, 9.1 miles S. of Moora on Mogumber Road (IBRA_AVW), 30°46'S, 116°01'E, 25 May 1954, B.Y. Main (WAM T139521); 1 ♀, 12.9 km NE. of New Norcia (IBRA_AVW), 30°55'00"S, 116°19'54"E, soil rake, leaf litter, 13 September 2012, T. Sachse (WAM T127016); 1 ♀, same data except 30°54'58"S, 116°19'54"E (WAM T127017DNA_Voucher_152); 1 juvenile, Watheroo National Park (IBRA_GES), 30°15'17"S, 116°00'13"E, 7 January 2010, B. Durrant (WAM T108031DNA_Voucher_148); 1 ♀, 4 miles E. of Watheroo (IBRA_AVW), 30°18'S, 116°07'E, 11 July 1955, B.Y. Main (WAM T144827); 1 ♀, same data (WAM T144828); 1 ♀, same data (WAM T144829).

Etymology.

The specific epithet is a noun in apposition, in reference to the occurrence of this species on the Dandaragan Plateau, north of Perth.

Diagnosis.

Idiosoma dandaragan 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. dandaragan can be further distinguished from those of I. arenaceum by the shape of the SP4 sclerites, which are not elongate-oval (Fig. 129; cf. Fig. 63); from I. kwongan by the absence of semi-circular lateral indentations adjacent to the SP4 sclerites (Fig. 129; 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. 124; cf. Fig. 27), and by the shape of the SP4 sclerites, which are circular or oval (Fig. 129; cf. Fig. 32). By our assessment, males of I. dandaragan are morphologically indistinguishable from those of I. schoknechtorum ; 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. 140, Key pane 23.2; 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. 140, Key pane 23.2; 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. 140, Key pane 23.2; cf. Figs 43, 52, Key pane 23.1), and by the presence of well-defined SP5 sclerites (Fig. 140, Key pane 23.2; cf. Figs 43, 52, Key pane 23.1) [NB. females of I. kwongan are unknown]. By our assessment, females of I. dandaragan are morphologically indistinguishable from those of I. schoknechtorum ; 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. 131; cf. Fig. 109), and by the shape of the female eye group, which is broadly trapezoidal (Fig. 139; cf. Fig. 117).

Description (male holotype).

Total length 17.5. Carapace 8.0 long, 5.7 wide. Abdomen 8.0 long, 5.6 wide. Carapace (Fig. 123) tan, with darker ocular region; lateral margins with uniformly-spaced fringe of porrect black setae; fovea procurved. Eye group (Fig. 126) 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 2.2 × 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 124, 129) oval, dark beige-brown in dorsal view with lateral sclerotic strips, dorso-lateral striations, and scattered dorsal sclerotic spots. Dorsal surface of abdomen (Fig. 124) more heavily setose anteriorly, with assortment of stiff, por rect black setae, each with slightly raised, dark brown sclerotic base. Posterior abdomen strongly sigillate (Figs 124, 129); SP2 sclerites irregular, comma-shaped spots; SP3 sclerites very large and circular; SP4 sclerites broadly oval; SP5 obscured. Legs (Figs 130-132) 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 6.9; patella 3.4; tibia 4.8; metatarsus 4.9; tarsus 2.9; total 22.9. Leg I femur–tarsus /carapace length ratio 2.9. Pedipalpal tibia (Figs 133-135) 2.3 × longer than wide; RTA burr-like, with conical basal protuberance and field of retroventral spinules; digital process porrect, unmodified. Cymbium (Figs 133-135) setose, with field of spinules disto-dorsally. Embolus (Figs 133-135) broadly twisted and sharply tapering distally, with prominent longitudinal flange and triangular (sub-distal) embolic apophysis.

Description (female WAM T127017).

Total length 18.6. Carapace 7.5 long, 5.3 wide. Abdomen 8.6 long, 8.3 wide. Carapace (Fig. 136) dark tan and chocolate-brown, with darker ocular region; fovea procurved. Eye group (Fig. 139) trapezoidal (anterior eye row strongly procurved), 0.7 × as long as wide, PLE–PLE/ALE–ALE ratio 2.3; ALE almost contiguous; AME separated by approximately their own diameter; PME separated by 2.8 × 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. 141); labium without cuspules. Abdomen (Figs 137, 140) 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. 140, Key pane 23.2) with truncate ‘shield-like’ morphology; SP3 sclerites very large and circular; SP4 sclerites broadly oval; SP5 sclerites small, broadly oval (left) or irregularly-shaped (right). Legs (Figs 142-143) variable shades of dark tan; scopulae present on tarsi and metatarsi I–II; tibia I with one stout pro-distal macroseta (broken off at base) and row of five longer retroventral macrosetae; metatarsus I with eight stout macrosetae; tarsus I with distal cluster of short macrosetae. Leg I: femur 4.7; patella 2.8; tibia 3.0; metatarsus 2.2; tarsus 1.6; total 14.3. Leg I femur–tarsus /carapace length ratio 1.9. Pedipalp tan, spinose on tibia and tarsus, with thick tarsal scopula. Genitalia (Fig. 144) with pair of short, obliquely angled spermathecae, each bearing dense field of glandular vesicles distally, and more sparsely distributed glandular field sub-distally.

Distribution and remarks.

Idiosoma dandaragan (formerly known by WAM identification code ‘MYG477’), a 'sigillate complex’ member of the diverse sigillatum-clade (Fig. 25), has a restricted distribution along the eastern margin of the Dandaragan Plateau, from near New Norcia in the south, north to at least the Watheroo National Park (Fig. 374). Its distribution closely abuts the north-western extent of the range of I. nigrum near New Norcia and Carani. Both I. dandaragan and I. nigrum are similar in having strongly sigillate (sclerotised) abdomens, although morphology and molecular data can be used to convincingly separate them. Little is known of the biology of this species, other than that males have been collected (wandering in search of females or waiting in their burrows) in late autumn.

Conservation assessment.

Idiosoma dandaragan has a known extent of occurrence of nearly 1,500 km2 [1,230 km2], and an area of occupancy within that range of <500 km 2. 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 western-central 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.