Gibbidessus davidi, 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 davidi sp. nov. Figs 3 , 4 , 12 , 16 , 23 , 27 , 28

Type locality.

Western Australia, Perth, suburb Success, Beeliar Regional Park, shallow peaty puddle [32°8'4S, 115°50'22E].

Type material.

Holotype, male: "Australia, WA, Perth, Success, Beeliar RP, shallow peaty puddle 32°8'4.97"S, 115°50'22.78"E 21.-31.10.2015 L. Hendrich (WA 1/15)", "Holotype Gibbidessus davidi Hendrich, Watts & Balke des. 2020" (WAM) [red printed label]. Paratypes (370 exs.). 354 specimens with same data as holotype (ANIC, CGC, CLH, SAMA, WAM, ZSM); 4 exs, "Australia: SW WA, D´Entrecasteaux NP, 11 km S, Northcliffe, 77m, 4.I.2007, 34.44.048S, 116.05.354E [34°44'0S, 116°5'13E], L. & E. Hendrich (WA 162)" (ZSM); 10 exs., "Australia, WA, Albany Hwy, Muir Lakes Nature Reserve, SW part of Byenup Lagoon, 4.& 5.1.2000, 34°30'4S, 116°44'19E, Hendrich leg. (loc. WA 11/157)" (CLH, ZSM); 1 ex., "Australia, WA, Barlee Brook Dickson Road (A) [34°12'17S, 115°46'18E], DON03, 21/10/2005, South West Forest Monitoring" (DPAW); 1 ex., "Australia, WA, Fish Creek (A) [34°37'29S, 116°26'11E], SHA22, 17/10/2010, South West Forest Monitoring" (DPAW); 4 exs., "Australia, WA, RVDLE03 Riverdale Wetland [32°59'23S, 115°47'23E], 23/09/2008, South West Catchment Council Mon." (DPAW). All paratypes with red printed paratype labels.

Diagnosis.

Small species which externally is characterised by a wide rounded body, shiny non-microreticulate dorsal surface, vague testaceous markings on elytra, and without habitus disruption between pronotum and elytron. Dorsoventrally rather domed. Cervical line present (Fig. 3 ).

Measurements.

Holotype: TL = 1.45 mm, TL-H = 1.35 mm, MW = 0.83 mm. Paratypes: TL = 1.35-1.5 mm, TL-H = 1.15-1.4 mm, MW = 0.8-0.9 mm.

Head: Ferruginous, around eyes almost black. Cervical line present (Fig. 12A ). Strongly and coarsely punctate, rather shiny, microreticulation present. Punctures weak anteriorly and strongly posteriorly between eyes. Antennae relatively short, stout. Antennomeres 1-8 ferruginous, 9-11 darkened anteriorly.

Pronotum: Ferruginous, anterior and posterior margins darker. Disc of pronotum somewhat darkened, broadest at posterior corners. Punctation of pronotum very weak, almost evenly distributed, shiny and microsculpture absent. Sides of pronotum margined and almost evenly rounded. Angle between pronotum and elytra less pronounced, basal pronotal plicae present. Striae moderately defined, almost 1/2 length of pronotum, strongly incurved.

Elytra: Dark brown with vague basolateral area ferruginous (Fig. 3 ). Coarsely and densely punctate, shiny, microsculpture absent. Striae deeply impressed, straight but shorter than basal pronotal striae.

Ventral side: Ferruginous. Prothorax and abdomen paler than other parts. Metacoxae and metaventrite covered with larger punctures, surface shiny, without microreticulation. Abdominal ventrites with dense and finer punctures, shiny, microreticulation absent. Metacoxal lines almost straight, anteriorly not divergent. Epipleuron ferruginous, with few coarse punctures, shiny, lacking microsculpture. Legs ferruginous with meta-/mesotibia and meta-/mesotarsi set in black.

Male. Smaller and more elongate than female (Fig. 4 ). Median lobe of aedeagus as in Fig. 16A, B . Shape of median lobe in lateral view, straight and fairly uniform, in ventral view broad, with a thorn on each side, and rounded at apex. Parameres bi-segmented and elongated with few setae at apex (Fig. 16C, D ).

Affinities.

This species is similar to G. atomus sp. nov. but readily separated by its larger size, the different colour pattern and the form of the median lobe and parameres (Figs 14 , 16 ). From G. pederzanii sp. nov. it can be distinguished by the less roundish body and the form of the median lobe and parameres (Figs 16 , 19 ).

Etymology.

The beetle is named after the son of the first author, David Hendrich. The specific epithet is a substantive in the genitive case.

Distribution.

South-western Australia. From Perth in the north to D´Entrecasteaux National Park in the south (Fig. 23 ).

Habitat.

In the Northcliffe area most specimens were obtained from an exposed, shallow and small roundish puddle, without any vegetation, except some algae. The other specimens were collected in a half-shaded pool in a Melaleuca blackwater swamp, with few clumps of Juncus spp. and extensive beds of macrophytes; depth up to 20 cm; bottom consisted of sedge-filled peat (pH 5.5), twigs and rotten leaves (Figs 27 , 28 ). The whole area south of Northcliffe is seasonally flooded with some permanent central water bodies in summer. In the D´Entrecasteaux NP the species is syntopic with G. atomus sp. nov., and around Perth in the Beeliar Regional Park with G. rottnestensis sp. nov. At the Riverdale Wetland Reserve G. davidi sp. nov. was syntopic with G. atomus sp. nov. and G. rottnestensis sp. nov.

Apart from the Gibbidessus , the water beetle coenosis at Northcliffe included the following species: Dytiscidae : Limbodessus inornatus , Antiporus hollingsworthi , A. mcraeae , Brancuporus gottwaldi , Sternopriscus minimus , S. eikei , Exocelina ater ; Hydrophilidae : Enochrus eyrensis , Limnoxenus zealandicus , Paracymus pygmaeus (see Hendrich 2001a). In the Beeliar Park the two Gibbidessus species share their habitat with Limbodessus inornatus , Paroster insculptilis (Clark, 1862), Exocelina ater , Rhantus suturalis (Macleay, 1825) and Rhantus simulans Régimbart, 1908.

Figures

Figure 12. Head of G. davidi sp. nov. A with cervical line (red arrow), and head of G. pederzanii sp. nov. B without cervical line but rather a few punctures instead (red arrow).

Figure 27. Habitat of Gibbidessus atomus sp. nov. and Gibbidessus davidi sp. nov. A Seasonally flooded Melaleuca sedge swamp B small and shallow heathland pool along Windy Harbour Road, south of Northcliffe, south-western Australia.

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.

Figures 1 - 4. Habitus of 1 Gibbidessus atomus sp. nov. 2 G. chipi, 3 G. davidi, male 4 G. davidi female. Scale bar: 1.0 mm.

Figures 16, 17. 16 Gibbidessus davidi sp. nov. 17 G. drikdrikensis 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 22, 23. Distribution of 22 Gibbidessus chipi (black dots), G. drikdrikensis sp. nov. (yellow square), G. kangarooensis sp. nov. (red square) 23 G. atomus sp. nov. (red square), G. davidi sp. nov. (yellow square).

Figures 14, 15. 14 Gibbidessus atomus sp. nov. 15 G. chipi A median lobe in ventral view B median lobe in lateral view, left side C left paramere in lateral view. Scale bar: 0.2 mm.

Figures 18, 19. 18 Gibbidessus kangarooensis sp. nov. 19 G. pederzanii 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.