Gibbidessus atomus, 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

publication ID	https://dx.doi.org/10.3897/zookeys.975.55456
publication LSID	lsid:zoobank.org:pub:785EDF22-5A32-4217-8C9B-6433E0AD199F
persistent identifier	https://treatment.plazi.org/id/713DD48F-BA41-4581-A05F-DEECAED51519
taxon LSID	lsid:zoobank.org:act:713DD48F-BA41-4581-A05F-DEECAED51519
treatment provided by	ZooKeys by Pensoft
scientific name	Gibbidessus atomus
status	sp. nov.

Treatment

Gibbidessus atomus sp. nov. Figs 1 View Figures 1–4 , 14 View Figures 14, 15 , 23 View Figures 22, 23 , 27 View Figure 27

Type locality.

Western Australia, Windy Harbour Road, 11 km south of Northcliffe, small pool in sedge swamp [34°48'51S, 116°4'8E].

Type material.

Holotype, male: "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)", "Holotype Gibbidessus atomus Hendrich, Watts & Balke des. 2020" [red printed label] (WAM). Paratypes (20 exs.). 7 specimens with same data as holotype, three specimens with "DNA M. Balke 1729", "DNA M. Balke 2780", "DNA M. Balke 2781" [green printed labels]; 13 exs., "AUSTRALIA/WA: D´Entrecasteaux N.P., 11 km south of Northcliffe, Windy Harbour Road, 50 m, 3.1.2000, 34°42'S, 116°05'E [34°44'0S, 116°5'13E], Hendrich leg. (loc. WA 10c/156)" (ANIC, CLH, SAMA, ZSM). All paratypes with red printed paratype labels.

Additional material.

1 ex., "Australia, WA, RVDLE03 Riverdale Wetland [32°59'22S, 115°47'7E], 23/09/2008, South West Catchment Council Mon." (DPAW).

Diagnosis.

Very small species, externally characterised by widely rounded body, with less pronounced habitus disruption between pronotum and elytron, shiny non-microreticulate dorsal surface and vague ferruginous markings on elytra. Dorsoventrally rather domed. Cervical line present (Fig. 1 View Figures 1–4 ).

Measurements.

Holotype: TL = 1.15 mm, TL-H = 1.05 mm, MW = 0.6 mm. Paratypes: TL = 1.15-1.30 mm, TL-H = 1.0-1.05 mm, MW = 0.6-0.65 mm.

Head: Dark brown, around eyes almost black. Cervical line present. Strongly and coarsely punctate, rather shiny, microsculpture almost absent. Punctures weakly distributed anteriorly, strong posteriorly between eyes. Antennae relatively short, stout. Antennomeres ferruginous, darkened anteriorly.

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

Elytra: Dark brown with vague basal area ferruginous (Fig. 1 View Figures 1–4 ). Coarsely and densely punctate, shiny, microsculpture absent. Striae weakly impressed, slightly straighter but shorter than 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 dense and finer punctures, shiny, microreticulation absent. Metacoxal lines almost straight, anteriorly slightly divergent. Epipleuron ferruginous, coarsely punctate, shiny, lacking microsculpture. Legs ferruginous with meta-/mesotibiae and meta-/mesotarsi set in black.

Male. Dorsal surface with coarse punctures but otherwise with shiny surface (Fig. 1 View Figures 1–4 ). Median lobe of aedeagus as in Fig. 14A, B View Figures 14, 15 . Shape of median lobe fairly uniform, bent evenly, apex straight and pointed. Paramere, as in Limbodessus Guignot, 1939, with hook or bent finger-like apical part with tiny setae on tip (Fig. 14C View Figures 14, 15 ).

Affinities.

This species is similar to G. davidi sp. nov. but readily separated by its smaller size, the different colour pattern and the form of the median lobe and parameres (Figs 14 View Figures 14, 15 , 16 View Figures 16, 17 ).

Etymology.

From Latin atomus (smallest particle), as it is the smallest epigean diving beetle in Australia described so far.

Distribution.

South-western Australia. Known only from the type locality in the D´Entrecasteaux National Park, south of Northcliffe and the Riverdale Wetland [32°59'22S, 115°47'7E] (Fig. 23 View Figures 22, 23 ).

Habitat.

Most specimens were obtained from an exposed, shallow and small roundish puddle without any vegetation, except some algae (Fig. 27B View Figure 27 ). The remaining specimens were collected in a half-shaded pool in a Melaleuca blackwater swamp (Fig. 27A View Figure 27 ), with few clumps of Juncus spp. and extensive beds of macrophytes; depth up to 20 cm; bottom of sedge-filled peat (pH 5.5), twigs and rotten leaves. The heathlands south of Northcliffe are seasonally flooded, with some permanent water bodies in the summer. At Northcliffe the species is syntopic with G. davidi sp. nov. ( Hendrich 2001a), at the Riverdale Wetland it was collected with G. davidi sp. nov. and G. rottnestensis sp. nov.

Apart from the Gibbidessus , the water beetle coenosis at Northcliffe included the following species: Dytiscidae : Limbodessus inornatus (Sharp, 1882), Antiporus hollingsworthi Watts, 1997, A. mcraeae Watts & Pinder, 2000, Brancuporus gottwaldi (Hendrich, 2001), Sternopriscus minimus Lea, 1899, S. eikei Hendrich & Watts, 2007, Exocelina ater (Sharp, 1882); Hydrophilidae : Enochrus eyrensis (Blackburn, 1895), Limnoxenus zealandicus (Broun, 1880), Paracymus pygmaeus (Macleay, 1871).