Gibbidessus rottnestensis, Hendrich & Watts & Balke, 2020

Hendrich, Lars, Watts, Chris H. S. & Balke, Michael, 2020, The " minute diving beetles " of southern Australia - taxonomic revision of Gibbidessus Watts, 1978, with description of six new species (Coleoptera, Dytiscidae, Bidessini), ZooKeys 975, pp. 11-49 : 11

Gibbidessus rottnestensis sp. nov. Figs 10 , 11 , 13 , 21 , 25 , 28 , 29

Uvarus pictipes (Lea, 1899): Watts (1978: 33, partim).

Type locality.

Australia, south-western Australia, Rottnest Island [32°0'22S, 115°30'26E].

Type material.

Holotype: Male, "W AUS, ca. 25 km N Augusta on Rd. 250, shallow pool, 4.11.2013, leg. Wewalka (A4)" "Holotype Gibbidessus rottnestensis Hendrich, Watts & Balke des. 2020" [red printed label] (WAM). Paratypes (27 exs.): 4 specimens with same data as holotype (CGW, ZSM); 3 males, 1 female "Rottnest Is. [32°0'22S, 115°30'26E] Oct´ 31 W.A.", "Australia, Harvard Exp., Darlington", "Museum of Comparative Zoology", " ANIC Database No. 25013255" (ANIC); 3 specimens with same data, and " SAMA Database No 25-00/596" (SAMA). 2 exs., "Australia, WA, Perth, Success, Beeliar RP, shallow peaty puddle 32°8'4S, 115°50'22E 21.-31.10.2015 L. Hendrich (WA 1/15)", "M. Balke 7248", "M. Balke 7247" [green, printed label] (ZSM); 1 ex., "Australia, WA, Albany Hwy, Muir Lakes Nature Reserve, SW part of Byenup Lagoon, 4. & 5.1.2000, 34°29'S, 116°44'E [34°30'4S, 116°44'19E], Hendrich leg. (loc. WA 11/157)" (CLH); 3 exs., "Australia, WA, 1 km W Kodjinup NP 34°24.03S, 116°38.37E [34°24'1S, 116°38'22E] 4.X.2003, CHS, Watts leg.", one specimen "M. Balke 3921" [green, printed label] (CLH, SAMA); 1 ex., "WA Kodjinup N.R. [34°23'10S, 116°39'30E] 21/9/00 C.H.S.Watts", " SAMA Database No 25-00/594" (SAMA); 2 exs., "AUSTRALIA, WA, Midlands, 38 Km ESE Cervantes, Wongonderrah Road, Nambung River Crossing, 9.9.2002, 30°33'21S, 115°21'27E, Hendrich leg. /Loc. 28b/192b" (CLH); 1 ex., "SW Australia/ N Bunbury, Yalgorup N.P. östl. Preston Beach [32°52'35S, 115°40'6E], 0m, 24.11.1996, Hendrich leg./Lok. 30" (CLH); 1 ex., "Australia, WA, RVDLE03 Riverdale Wetland [32°59'22S, 115°47'7E], 23/09/2008, South West Catchment Council Mon." (DPAW); 1 ex., "Australia, WA, Pindicup Lake [34°24'35S, 116°43'20E], MUB030, 29.09.2014, Muir-Byenup Survey, M. Pennifold leg." (DPAW); 1 ex., "Australia, WA, Pindicup Lake [34°24'35S, 116°43'20E], MUB030, 25.09.2014, Muir-Byenup Survey, M. Pennifold leg." (DPAW); 2 ex., "Australia, WA, wetland north of Mialla Lagoon [33°10'04S, 115°44'01E], MIAL01, 8/10/2007, South-west Catchment Council Wetland Monitoring" (DPAW). All paratypes are provided with red printed paratype labels.

Note.

Watts (1978: 33) reports Uvarus pictipes from Rottnest Island (housed in Museum of Comparative Zoology and SAMA); these specimens belong to Gibbidessus rottnestensis sp. nov.

Diagnosis.

Larger species which externally is characterised by a more elongate body, shiny non-microreticulate dorsal surface, testaceous markings on elytra, and with distinct habitus disruption between pronotum and elytron. Dorsoventrally slightly flattened. Without cervical line but rather a few punctures instead (Fig. 10 ).

Measurements.

Holotype: TL = 1.85 mm, TL-H = 1.65 mm, MW = 0.95 mm. Paratypes: TL = 1.7-1.9 mm, TL-H = 1.5-1.7 mm, MW = 0.85-1.0 mm.

Head: Black to ferruginous, without cervical line but rather a few punctures instead (punctures not obvious in females) (Fig. 13B ). Evenly and coarsely punctate, shiny but with weak microreticulation. Punctures weak anteriorly and stronger posteriorly between eyes. Antennae relatively short, stout. Antennomeres 1-3 ferruginous, 4-11 darkened anteriorly.

Pronotum: Ferruginous, anterior and posterior margins darker. Broadest at middle. Punctation very strong, almost evenly distributed, shiny and microsculpture absent. Sides of pronotum broadly margined and almost evenly rounded. Angle between pronotum and elytra well pronounced, basal pronotal plicae present. Striae moderately defined, almost 1/2 length of pronotum, strongly incurved.

Elytra: Dark brown to black, with distinct basal and subapical testaceous markings (Fig. 10 ). Coarsely and densely punctate, shiny, microsculpture absent. Striae weakly impressed, slightly incurved and of same length as basal pronotal striae.

Ventral side: Ferruginous. Prothorax and apex of abdomen paler than other parts. Metacoxae and metaventrite covered with numerous larger punctures, surface shiny, without microreticulation. Abdominal ventrites with finer punctures, shiny, microreticulation absent. Metacoxal lines almost straight, anteriorly slightly divergent. Epipleuron ferruginous, coarsely punctate, shiny, lacking microsculpture. Legs ferruginous with meta-/mesotibia and meta-/mesotarsae somewhat darkened.

Male. Dorsal surface with coarse punctures but otherwise with shiny surface (Fig. 10 ). Median lobe of aedeagus as in Fig. 21A, B . Shape of median lobe, bent evenly and fairly uniform in lateral view, in ventral view strongly tapering and rounded at apex. Parameres bi-segmented, elongated, without setae inside apical hook (Fig. 21C, D ).

Female. Dorsal surface almost mat, with coarse punctures and dense microreticulation (Fig. 11 ).

Affinities.

This species is similar to the smaller G. pictipes (TL = 1.45-1.6 mm) but readily separated by the different colour pattern on elytra. Furthermore, both species can be separated by the form of their median lobes and parameres (Figs 20 , 21 ).

Etymology.

The species is named after the type locality. The specific epithet is a substantive in the genitive case.

Distribution.

South-western Australia. Widespread but always rare and in low population densities. A more coastal species, from around 100 km north of Perth to south of Augusta and eastwards to the Muir Lakes (Fig. 25 ).

Habitat.

Seasonal, very shallow and exposed sedge swamps, pool and puddles on sandy bottom, with a thin layer of peat and rotten debris of sedges (Figs 28 , 29 ). Gibbidessus rottnestensis sp. nov. tolerates slightly saline water as it was found at Preston Beach in a shallow lagoon near the coast. According to the data it is an early spring breeder. Most specimens were collected in September and October. In the Riverdale Wetland the species was syntopic with Gibbidessus atomus sp. nov. and G. davidi sp. nov. For the rich water beetle coenosis in Beeliar Regional Park near Perth see under Gibbidessus davidi sp. nov. In the seasonal swamps at Wongonderrah Road, near Nambung River Crossing, the species was collected with several hundred specimens of an undescribed Exocelina species and Hyderodes crassus Sharp, 1882; at Preston Beach north of Bunbury it was collected with Hyphydrus elegans (Montrouzier, 1860), Necterosoma darwinii , and Platynectes aenescens Sharp, 1882.

Figures

Figure 13. Head of G. pictipes A without cervical line (red arrows), and of G. rottnestensis sp. nov. B without cervical line but rather a few punctures instead (red arrows).

Figure 28. Habitat of Gibbidessus davidi sp. nov. and Gibbidessus rottnestensis sp. nov. A Shallow peaty pool with mats of floating grasses along Beeliar Swamps in Perth B same spot and habitat details with collecting methods.

Figure 29. Habitat of Gibbidessus rottnestensis sp. nov. A and B seasonally flooded wetlands at Wongonderrah Road, Nambung River Crossing, 38 Km ESE Cervantes.

Figures 8 - 11. Habitus of 8 G. pictipes, male 9 G. pictipes, female 10 G. rottnestensis sp. nov., male 11 G. rottnestensis sp. nov., female. Scale bar: 1.0 mm.

Figures 20, 21. 20 Gibbidessus pictipes 21 G. rottnestensis sp. nov. A median lobe in ventral view B median lobe in lateral view, left side C left paramere in lateral view, D right paramere in lateral view. Scale bar: 0.2 mm.

Figures 24, 25. Distribution of 24 Gibbidessus pictipes (black dots) 25 G. pederzanii sp. nov. (red dot), G. rottnestensis sp. nov. (blue dots).