Gymnochthebius trilineatus, 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 trilineatus new species

(Figures 29, 30, 77)

Type Material. Holotype (male): Australia: Victoria: Victorian Alps [no date], Blackburn. Deposited in the SAMA . Paratypes (23): Australia: Australian Capital Territory: Casuarina Sands on Murrumbidgee River, coarse sand, gravel and roots (Casuarina) at edge of riffle zone of large river; Casuarina riparian forest, elev. 475 m, 35° 19' S, 148° 57' E, 21 July 2000, N. Porch (NP 69) (1 ANIC) ; Kambah Pool , 35° 24' S, 149° 1' E, 26 November 1998, C. Watts (1 SAMA) ; Queensland: Albert River, ca. 30 m a.s.l., and Dunn Creek (residual pool in tributary of Albert River ) at Alan Wilke Bridge , S of Wolfdene [or Wolffdene acc. to other sources], ca. 30 km SE Brisbane [beeline], 27° 46’34.7”S 153° 11’ 07.2”E, River ( Albert River ), ca. 20 m wide, slightly polluted, flowing through cultivated land, 21 August 2004, M. A. Jäch (AU 3) (12 NMW) ; Dayboro , 2 km S, in moist soil, dry river bed, 27° 13' S, 152° 50' E, 12 October 1991, T. Gush (1 ANIC) ; Kilcoy , 11 km E, in creek debris, 26° 56', 152° 40' E, 19 October 1991, T. Gush (7 ANIC) ; Running Creek, along road between Mt. Chinghee NP and Border Ranges NP, at Seventh Bridge , ca. 40 km [beeline] S Beaudesert, 28° 19’13.2”S 152° 55’ 39.1”E, River ( Running Creek ), ca. 5–8 m wide, incl. rockpools, through open forest (Casuarina, Eucalypt), 25 August 2004, M. A. Jäch (AU 13) (1 NMW) . Representative specimens to be deposited in MCZ, NPC, and QMBA .

Differential Diagnosis. Recognized by the very convex form, the shining dorsum, the finely sparsely punctate pronotum contrasting with the strongly punctate and striateimpressed elytral series, and especially the confluent pronotal anterior and posterior foveae, forming a narrow sinuate line on each side of the median groove. Distinguished from G. nicki , which is also quite convex dorsally, by the confluent pronotal foveae (Figs. 29, 31). The male genitalia of the two species show some similarity, both lacking barbs, but the parameres are much longer and stronger and the lobes more sharply pointed in G. trilineatus (Figs. 30, 32). Distinguished from G. bacchusi (Fig. 33), which also has confluent pronotal foveae, by the less transverse and more convex pronotum, the striateimpressed elytral punctures, the shorter setae of the elytral punctures, and the fringe of setae on the elytral lateral margins.

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.67/ 0.78; head 0.33/0.44; pronotum 0.44/0.57; elytra 1.07/0.78. Form moderately ovate, rather strongly convex. Color brown, head darker, dorsal reliefs highly shining.

Frons very finely sparsely punctate, very sparsely pubescent on disc, more setose laterally; interocular foveae deep; interocular tuberculi distinct; basal fovea confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5 apical width, very sparsely punctate; setae very sparse on disc, distinctly denser laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width 3x length; anterior margin arcuate, with very small 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 angle acute point, lateral margin weakly arcuate, with short fringe of setae; lateral fossulae deep, lacking microsculpture; pronotal disc transversely quite convex, extremely finely sparsely punctate, most punctures with a minute recumbent seta; median groove deep, narrow, extending nearly to margins, tapering at ends; anterior and posterior foveae slightly narrower than median groove, joined by narrow channel to form slightly sinuate groove; posterolateral angles without shallow impressions.

Elytra very convex on disc, with six rows of deep, slightly elongate, closely spaced punctures in shallow striae between suture and humeri; most punctures without a perceptible seta; intervals rounded, width 1.0–1.5x that of punctures; even numbered intervals with widely spaced very short setae in unilinear row; summit of declivity slightly in front of midlength, where elytra are transversely markedly convex; explanate margin nearly nonexistent; margin with fringe of very short setae.

Metasternal glabrous area length equal width, oval, shining, convex. Abdominal ventrites 1–3 with hydrofuge pubescence.

Aedeagus (Fig. 30): Length of main­piece 0.30 mm, length to tip of parameres 0.36 mm; lobes relatively long, each tapering, not barbed; parameres widened and strong apically, setae stout.

Females have the elytral explanate margin similar to that of males; the labrum anterior margin is arcuate, lacking the minute tooth present in males.

Etymology. Named in reference to the three impressed lines on the pronotum.

Distribution. Currently known from two widely disjunct areas, one each in the Australian Capital Territory and Queensland, and the type locality, "Victorian Alps" (Fig. 77).