Gymnochthebius sexplanatus, 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 sexplanatus new species

(Figures 48, 49, 73)

Type Material. Holotype (male): Australia: Western Australia: Murchison R., 27° 49' S, 114° 41' E, 28 March 1971, E. F. Riek. Deposited in the ANIC . Paratypes: Same data as holotype (32 ANIC). Representative specimens to be deposited in MCZ, NPC, SAMA, and WAMP .

Differential Diagnosis. Recognized by the elongate body form and legs, the large and deep pronotal foveae, the shining dorsal reliefs, and the striate­impressed elytral series. Females have the explanate elytral margin about twice as wide as it is in males, and markedly arcuate. Most similar in dorsal habitus to G. coruscus (Figs. 44, 48), but the male genitalia of the two species differ markedly in shape of the main­piece and in paramere setae (Figs. 45, 49).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 2.04/ 0.82; head 0.37/0.52; pronotum 0.48/0.67; elytra 1.30/0.82. Form moderately ovate, moderately convex. Color light brown to testaceous, head darker, dorsal reliefs shining.

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 apically, more coarsely punctate basally; pubescence very sparse on disc, slightly more developed laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum length:width as 5:13, moderately pubescent, anterior margin arcuate, with prominent apicomedian upturned 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 nearly straight in midregion; each lateral depression with posterior angle obtuse, lateral margin arcuate from anterior angles, then emarginate in front of posterior angle, sparsely setose; lateral fossulae deep, terminating anteriorly in pit, very effacedly microreticulate; pronotal disc moderately convex, sparsely moderately finely punctate, most punctures without discernible setae; median groove moderately deep and wide, not attaining margins, tapering at ends; anterior foveae well developed; posterior foveae oblique, linear impressions slightly greater than 1/2 as long as and slightly wider than median groove; posterolateral angles with indistinct shallow impressions.

Elytra weakly convex on disc, with six rows of closely spaced punctures in well developed striae between suture and humeri, each puncture with short inconspicuous seta; intervals rounded, width equal that of punctures; posterior declivity gradual, summit slightly behind midlength; striae 2 and 3 terminating into 4 at about apical 0.15; elytral margin very narrow, lacking prominent setae.

Metasternal glabrous area longer than wide (as 19:14), elongate oval, shining, convex. Abdominal ventrites 1–3 and basal part of 4 with hydrofuge pubescence.

Aedeagus (Fig. 49): Length of main­piece 0.39 mm, length to tip of parameres 0.46 mm; lobes relatively short, strongly barbed; apical paramere seta much longer than other setae.

Females have the explanate elytral margin markedly arcuate, about twice as wide as it is in males, widest slightly in front of midlength, slightly wider than the mesotibia; the anterior margin of the labrum is weakly apicomedially emarginate.

Etymology. Named in reference to the sexually dimorphic explanate margins of the elytra.

Distribution. Currently known only from the type locality in far western Western Australia (Fig. 73).