Gymnochthebius tenebricosus (Deane) 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 tenebricosus (Deane) new combination

(Figures 39, 84)

Ochthebius tenebricosus Deane, 1931: 169 .

Type Material. Lectotype (hereby designated; female): Australia: New South Wales: Sydney [labels: "North Sydney flood refuse 9.06 HJC"; "Type T­4192"]. Deposited in the MVMA. The type series in the Museum of Victoria consists of two female specimens. I have selected one specimen to serve as lectotype and have affixed a label indicating such. In the second specimen the pronotal foveae are longitudinally, broadly confluent, whereas in the lectotype there is only the faintest indication of a shallow depression linking the foveae.

Differential Diagnosis. Recognized from other species with dull dorsum and similar abdominal hydrofuge pubescence pattern ( G. brisbanensis and G. fumosus ) by the angulate lateral margins of the pronotum, the black color, and the more distinctly striate­impressed elytral series (Figs. 35, 37, 39). Males are unknown.

Description. Size (length/width, mm) lectotype: body (length to elytral apices): 1.56/0.72; head 0.32/0.44; pronotum 0.40/0.60; elytra 1.00/0.72. Form moderately ovate, moderately convex. Color black, entire dorsal surface dull.

Frons very finely sparsely punctate, very sparsely pubescent; interocular foveae deep; interocular tuberculi distinct; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5x apical width, very sparsely punctate; pubescence very sparse on disc, slightly more developed laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width twice length, anterior margin broadly and shallowly emarginate, almost straight.

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 slightly produced in midregion; each lateral depression with posterior angle produced as acute point, lateral margin setose, distinctly produced to an obtuse point slightly anterior to midlength; lateral fossulae deep, microsculpture similar to remainder of pronotum; pronotal disc moderately convex, extremely finely sparsely punctate, each puncture with a recumbent yellow seta which contrasts with black cuticle; median groove shallow, very narrow, extending nearly to margins, tapering at ends; anterior foveae well developed; posterior foveae oblique, linear impressions nearly 1/2 as long as and twice as wide as median groove; posterolateral angles each with shallow impression.

Elytra moderately convex on disc, with six rows of punctures in well developed striae between suture and humeri; punctures round, separated from each other by about puncture width; intervals rounded, width twice that of punctures; summit of declivity slightly behind midlength; striae 2 and 3 terminating into 4 at about apical 1/4; elytral margin lacking prominent setae.

Prosternum lacking midlongitudinal carina. Metasternal glabrous area large, dull similar to pronotum. Abdominal ventrites 1–3 and anterior 0.33 of 4 with hydrofuge pubescence; other sterna dull, lacking hydrofuge pubescence.

Aedeagus: Male unknown.

Distribution. Although described more than seventy years ago, this species is still known only from the two female type specimens, collected in "north Sydney" (Fig. 84).