Gymnochthebius radiatus, Perkins, 2005

Perkins, Philip D., 2005, A revision of the water beetle genus Gymnochthebius Orchymont (Coleoptera: Hydraenidae) for Australia and Papua New Guinea, Zootaxa 1024 (1), pp. 1-161 : 1-161

Gymnochthebius radiatus new species

(Figures 25, 26, 74)

Type Material. Holotype (male): Australia: Northern Territory: Roderick Creek, Gregory N.P., M. V. Light, Operation Raleigh 1986, 15° 38' S, 131° 22' E, 4–6 July 1986, I. Archibald. Deposited in the MAGD.

Differential Diagnosis. A highly shining species recognized by the pronotum with only the faintest indication of a median groove, the absence of posterior foveae, the striateimpressed elytral series, and the large, subrhomboidal metasternal glabrous area. Distinguished from G. lustrosulcus , the only other species lacking posterior pronotal foveae, by the obsolete pronotal median groove, the larger lateral depressions of the pronotum, and the wider, slightly more convex body form (Figs. 25, 27). Both species have the abdominal hydrofuge pubescence reduced to lateral areas of the first and second ventrites. The male genitalia of the two species bear some resemblance, but differ in several details, including shapes of the lobes and duct (Figs. 26, 28).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.52/ 0.78; head 0.30/0.44; pronotum 0.41/0.63; elytra 1.00/0.78. Form moderately ovate, convex, especially transversely convex on elytra. Color dark brown, marginal band on elytra (modified explanate margin visible in lateral aspect), lighter reddish­brown; dorsal surface very shiny, non­microreticulate.

Head shiny, frons very finely sparsely punctate; interocular foveae deep, transverse; interocular tuberculi distinct, transverse; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength equal apical width, very sparsely punctate, very sparsely pubescent. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width slightly greater than length, anterior margin arcuate, small depression in midline behind margin.

Pronotum lateral hyaline border well developed, origin at base of lateral depression, arcuate to posterior angles, very narrow around posterior margin; anterior margin of pronotum bisinuate; each lateral depression weakly convex, posterior margin weakly concave, posterior angle sharp, not produced to form small point, lateral margin arcuate, densely setose; lateral fossulae shallow, lacking distinct microsculpture but slightly less reflective than surrounding area; pronotal disc transversely convex, very shiny, extremely finely sparsely punctate, almost glabrous, each puncture with a minute recumbent seta; median groove almost absent, very faint line interrupted in midlength; anterior foveae very small, transverse incisions, each confluent with respective lateral fossula; posterior foveae absent; posterolateral angles lacking impressions.

Elytra very transversely convex on disc, with six rows of punctures in shallow striae between suture and humeri; intervals shiny, weakly rounded, width 2–3 times that of punctures; punctures very small, slightly elongate, separated from each other by about puncture length, each with a minute seta; summit of declivity at or slightly in front of midlength; sides of elytra nearly vertical in posterior 1/4, apices conjointly sharply rounded; striae 3 and 4 confluent at about apical 1/4; margin not explanate, area flat and wide (in lateral aspect), with distinctive dense fringe of setae.

Metasternal glabrous area slightly wider than long, subrhomboidal. Abdominal ventrites 1 and 2 with hydrofuge pubescence laterally, absent medially.

Aedeagus (Fig. 26): Length of main­piece 0.28 mm, length to tip of parameres 0.29 mm; lobes relatively long, not barbed, but bent slightly apically; notch narrow, narrowest apically; apical paramere setae much longer than other setae.

Females unknown.

Etymology. Named in reference to the highly shining dorsum.

Distribution. Currently known only from the type locality in Gregory National Park, Northern Territory (Fig. 74).