Gymnochthebius truncatus, 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 truncatus new species

( Figures 7 , 8, 74)

Type Material. Holotype (male): Australia: Queensland: Cape York, Archer River, Archer Bend , moderately large shallow billabong/pool in otherwise dry river bed; unvegetated with thick layer of dead leaves etc., 13° 28' S, 142° 12' E, 28 September 1983, C. Watts. Deposited in the SAMA . Paratypes (23): Australia: Northern Territory: Kakadu NP, Malapanbanjo Ck , c. 8 km S of Arnhem Hwy on Pine Creek Rd., 12° 16' S, 132° 40' E, M. B. Malipatil (1 MAGD) ; Nourlangie Creek , 8 km. E of Mt. Cahill, mud at edge of waterhole, 12° 52' S, 132° 47' E, 27 October 1972, E. B. Britton (15 ANIC) ; Queensland: 10 km WNW of Rokeby ( Mango Lagoon ), lagoon with rocks at edge, 13° 38' S, 142° 35' E, 27 October 1992, P. Zborowski, T. Weir (2 ANIC) ; Cape York, Archer River, Archer Bend , moderately large shallow billabong/pool in otherwise dry river bed; unvegetated with thick layer of dead leaves etc., 13° 28' S, 142° 12' E, 28 September 1983, C. Watts (4 SAMA) ; Ling Creek , watersweep, 12° 19' S, 142° 10' E, 14 August 1993, P. Zborowski & J. Balderson (1 ANIC) . Representative specimens to be deposited in MCZ and NPC .

Differential Diagnosis. Recognized by the truncate body form, the shining dorsum, the shallowly striate­impressed elytral series, the large, shining, subrhomboidal metasternal glabrous area, and the abdominal ventrites 1–2 and basally 3 with hydrofuge pubescence. The dorsal sculpture is somewhat similar to that of G. angulonotus , but the two species differ in body proportions and size ( Figs. 5 , 7 ). The male genitalia have two barbs on each lobe, as does G. levis , but the two species differ in most other genitalic characters and are so different externally as to defy comparison.

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.49/ 0.71; head 0.30/0.44; pronotum 0.33/0.59; elytra 0.94/0.71. Form moderately ovate, moderately convex. Color dark brown, legs lighter, dorsal reliefs moderately shining. Frons very finely sparsely punctate, very sparsely pubescent; interocular foveae deep; interocular tuberculi distinct; basal midlongitudinal fovea confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5 apical width, very sparsely punctate; pubescence sparse on disc, denser laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width twice length; anterior margin arcuate, with very low upturned apicomedian tooth.

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 arcuate in midregion; each lateral depression with posterior in form of right angle, lateral margin distinctly setose; lateral fossulae deep, lacking microsculpture; pronotal disc moderately convex, extremely finely sparsely punctate, each puncture with a recumbent seta; median groove moderately deep, narrow, extending nearly to margins, tapering at ends; anterior foveae shallow, sides gradually sloping; posterior foveae oblique, shallow, linear impressions nearly 1/2 as long as and as wide as median groove, sides gradually sloping; posterolateral angles without impressions.

Elytra convex on disc, with six rows of slightly elongate, closely spaced punctures in shallow striae between suture and humeri; each puncture with a decumbent seta that overlaps base of following seta; intervals slightly rounded, width 2–3x that of punctures; summit of declivity at midlength; explanate margin narrow, with fringe of long setae.

Metasternal glabrous area length less than width (as 14:20), subrhomboidal, anteriorly nearly attaining intercoxal process, shining, convex. Abdominal ventrites 1–2 and basally 3 with hydrofuge pubescence.

Aedeagus ( Fig. 8): Length of main­piece 0.25 mm, length to tip of parameres 0.26 mm; lobes relatively long and slender, each with two barbs; dorsal notch U­shaped, widest apically, slightly deeper than ventral notch; apical paramere seta elongate, much longer than other setae.

Females have the elytral explanate margin similar to that of males; the anterior margin of the labrum is arcuate.

Etymology. Named in reference to the body form.

Distribution. Currently known from northern Queensland and northern Northern Territory (Fig. 74).

Figures

FIGURE 5. Gymnochthebius angulonotus, holotype. Dorsal and lateral habitus.

FIGURE 7. Gymnochthebius truncatus, holotype. Dorsal and lateral habitus.