Ariadna phantasma sp. nov.

Figs 1a–j, 2a–j, 3a–d

http://zoobank.org/ urn:lsid:zoobank.org:act: AA5C8AB4-899D-4740-BD54-4950A8C3A1C6

Type material. Holotype male. AUSTRALIA: Western Australia: Lake Cowan, - 31.8928°S, 121.7022°E; 01 October 2019; spotlighting at night; P. Hudson, H. Atkin (WAM T152196). Paratype female. Same data as the holotype, except - 32.1846°S, 121.7267°E, excavated from burrow, 29 September 2019, P. Hudson (WAM T152192).

Other material examined. Juvenile, same data as holotype male (WAM T152195); juvenile same data as holotype male, except - 32.0585°S, 121.6832°E, excavated from burrow, P. Hudson (WAM T152193); juvenile, except - 32.0585°S, 121.6832°E, excavated from burrow, P. Hudson (WAM T152194).

Etymology. The specific name is taken from Ancient Greek, meaning spectre/ phantom and refers to the distinctive pale, ghostly colouration of this species. It is a feminine noun in apposition.

Diagnosis. Males of this species can be differentiated from all other Australian currently named species of Ariadna by the combination of the pale colour (Figs 1a, b, c cf. Baehr & Whyte 2016, fig. 3a–c; Hickman 1929; Hogg 1900; Marsh et al. 2018, fig. 1a, b; 2a, b; Simon 1893b); the cluster of around 12 macrosetae prolaterally on femur I, where currently described species have three or fewer (Fig. 1f cf. fig. 3b, f Baehr & Whyte 2016; fig 1d, 4f Marsh et al. 2018), and a preening comb on metatarsi IV with just two spines (Fig. 1e cf. figs 1e, 2d Marsh et al. 2018). The female can be further differentiated from all other Australian currently named Australian species by the pale colour (Figs 2a, b, c cf. Hickman 1929; Hogg 1900; L. Koch 1873; Lamb 1911; Main 1954; Marsh et al. 2018, fig. 1a, b; 2a, b; Pocock 1900; Rainbow 1920; Simon 1893b; Simon 1908); by a lack of ventral macrosetae on tibia and metatarsi I and II (Figs 2i, j cf. Marsh et al. 2018; Hickman 1929; Hogg 1900; L. Koch 1873; Lamb 1911; Main 1954; Marsh et al. 2018 figs 2d, f, 3d, e; Pocock 1900; Rainbow 1920; Simon 1893b; Simon 1908) and by a preening comb with just two spines (Fig. 2e cf. figs 2h, 3h Marsh et al. 2018).

Description (holotype male). Total length 7.0

Colour in ethanol: Carapace white-cream, with faint, darker cream striations extending from the fovea (Fig. 1a), sternum white-cream, with orange-cream at perimeter and on precoxal sclerites, labium, maxillae and chelicerae white cream (Fig. 1b), abdomen dorsally mid grey (Fig. 1a), ventrally mottled pale, white grey (Fig. 1b), legs white, dark grey apically on tarsi (Figs 1f, g).

Cephalothorax: 3.4 long, 2.3 wide, 1.4 high. Carapace shield-shaped, narrower anteriorly, fovea a shallow indentation (Fig. 1a), carapace flattened in lateral view, highest at eyes (Fig. 1c). Labium narrowed anteriorly, about ¾ length of maxillae (= endites); sternum oval, with precoxal triangles and with smaller, broadly-triangular intercoxal extensions (Fig. 1b); chelicerae with basal transverse ridge, retromargin with single tooth, promargin with three teeth. Posterior eye row moderately recurved (Fig. 1d).

Abdomen: 3.6 long, with sparse grey setae.

Legs: Leg length ratio II>I>IV>III; leg I femur 3.6, patella 1.1, tibia 2.6, metatarsus 2.6, tarsus 0.8, total 10.7; leg II femur 3.5, patella 1.2, tibia 2.9, metatarsus 2.6, tarsus 0.9, total 11.1; leg III femur 2.7, patella 0.6, tibia 1.7, metatarsus 2.7, tarsus 1.0, total 8.7; leg IV femur 3.3, patella 1.2, tibia 2.6, metatarsus 2.0, tarsus 0.8, total 9.9. Femur I bowed in dorsal view (Fig. 1a). Macrosetae: Femora of all legs with numerous non-serial setae, prolaterally and dorsally, variable between both sides of the spider; leg I Femur with numerous non-serial setae prolaterally and dorsally, p7, d11, rd3; tibia r1-1-1-1-1, vr1-1-1-1ap, p1-1-1-1-1-1, vp1-1-1-1-1; metatarsus p1-1, vp1-1-1, r1-1-1, vr1-1; leg II Femur rd2, d8, pd4, patella p1-1-1, r1, tibia p1-1-1-1, pv1-1-1-1, rv1-1-1-1-1, r1-1-1-1-1; metatarsus p1-1-1-1-1, r1-1-1; leg IV: femur d12, vd2ap, tibia rv1-1, v1ap, metatarsus v1, v3ap (Figs 1f, g). Retrolateral preening comb on metatarsi IV with 2 macrosetae (Fig. 1e). Superior tarsal claws with 14 long teeth, inferior tarsal claw with small tooth. Tarsi with sparse distoventral scopulose setae.

Pedipalp: Pedipalp tibia width about 1/3 of length, cymbium with anterior prolateral extension, scopulose setae anteriorly; bulb large, globular in lateral view, embolus short, tapering and hooked apically (Figs 1h–j).

Description (paratype female). Total length 8.3

Colour in ethanol: Carapace white-cream, darker cream anteriorly (Fig. 2a); sternum white-cream, with orangecream at perimeter and on precoxal sclerites; labium, maxillae and chelicerae pale orange-cream (Fig. 2b). Abdomen dorsally light grey (Fig. 2a), ventrally pale cream (Fig. 2b). Legs pale cream, with legs I and II darker cream, with cream-brown on tarsi and metatarsi (Fig. 2h, i).

Cephalothorax: 4.0 long, 2.5 wide, 1.7 high. Carapace oval, narrower anteriorly, with sparse covering of fine dark setae, fovea a shallow indentation (Fig. 2a); carapace slightly domed in lateral view, highest just posterior to eyes (Fig 2c). Sternum oval, with precoxal triangular extensions, with fine dark setae, labium narrowed anteriorly, about ¾ length of maxillae (Fig. 2b). Chelicerae with basal transverse ridge, retromargin with single tooth, promargin with three teeth. Posterior eye row straight (Fig. 2d).

Abdomen: 4.3 long, with sparse grey setae.

Legs: Leg length ratio II>I>IV>III; leg I femur 3.2, patella 1.4, tibia 2.4, metatarsus 2.0, tarsus 1.0, total 10.0; leg II femur 3.5, patella 1.2, tibia 2.9, metatarsus 2.6, tarsus 0.9, total 11.1; leg III femur 2.7, patella 0.6, tibia 1.7, metatarsus 2.7, tarsus 1.0, total 8.7; leg IV femur 3.3, patella 1.2, tibia 2.6, metatarsus 2.0, tarsus 0.8, total 9.9. Femur I bowed in dorsal view. Macrosetae: Femora of all legs bare, leg I metatarsus p1-1ap, r1ap; leg II p1-1ap, r1ap; leg IV metatarsi retrolateral preening comb with two macrostetae and a separate macroseta adjacent to the pair. Superior tarsal claws with 8 teeth, inferior tarsal claw with small tooth.

Genitalia: Epigastrium a slightly raised, very lightly sclerotized external plate. Anterior receptaculum bilobed; ventral lobe smooth and gently sinuous; about 3/4 the length of the dorsal lobe (Figs 2g, h).

Biology. The open burrows of A. phantasma sp. nov. are readily distinguished from those of other spiders inhabiting the surface of Lake Cowan by the presence of distinctive web in the mouth of the burrow (see Figs 3a–c). The mud excavated in creating the burrow is sometimes arranged in a low ring around the entrance or dispersed as pellets some distance from the burrow. In contrast, for example, salt lake inhabiting wolf spiders in the genus Tetralycosa Roewer 1960 distribute the mud pellets around the burrow and silk is not discernible on the entrance (Framenau and Hudson, 2017). The burrows of A. phantasma sp. nov. were vertical, some 10–15cm deep. This species was collected in September/October by excavating burrows and whilst spotlighting. At that time burrows were quite abundant. Lake Cowan has been visited in several other years by PH in March/April but no segestriids were observed, nor were they observed on any other nearby lakes visited during September/October. It is suspected that the lack of March/April records may be due to the burrows being sealed to escape the harsh summer conditions.

Conservation status. This species is known only from Lake Cowan (Western Australia). Research on Ariadna in Australia shows that species in the genus typically have a restricted distribution (JRM, pers. obs.), and many likely qualify as short-range endemics and as such of subsequent conservation concern (Harvey 2002; Harvey et al. 2011). The highly specialised habitat of this species suggests that even if it occurs in areas external to Lake Cowan, it is confined to salt lake / saline habitats and as such has a restricted Extent of Occurrence (EOO). Several threats are posed to salt lake species in Western Australia, including driving of vehicles on the salt lake (Fig. 3d); excessive discharge of saline water on to the lakes; decreasing groundwater levels; the mining of salt lakes for minerals and future higher temperatures and reduced rainfall as a result of climate change. The restricted EOO of Ariadna phantasma sp. nov., in combination with threats posed to its habitat, which are likely to further reduce EOO and habitat quality, make the species of conservation importance, and we recommend it as a candidate for consideration for inclusion in the IUCN Red List (IUCN Standards and Petitions Committee, 2019).