Gymnochthebius semicylindrus, 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 semicylindrus new species

( Figures 17 , 18 , 93)

Type Material. Holotype (male): Australia: South Australia: Cygnet R. Turkey Lane, 35° 46' S, 137° 10' E, 23 June 1994, Aust. water quality centre 3710. Deposited in the SAMA.

Differential Diagnosis. Recognized by the narrow and transversely convex, semicylindrical, body form, the bisinuate margins of the lateral depressed areas of the pronotum, the large, serially closely spaced elytral punctures, and the black color. This species shows some resemblance to G. wattsi , but is distinguished there from by the larger size (ca. 1.86 v. 1.75), the more convex body form, the non­confluent pronotal foveae, the bisinuate lateral margins of the pronotum, and the coarser punctation. The male genitalia of the two species also suggest a relationship, but differ significantly in the shape and size of the duct, the shape of the lobes, the length and shape of the parameres, and form of the paramere setae ( Figs. 16, 18 ).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.86/ 0.75; head 0.37/0.48; pronotum 0.41/0.65; elytra 1.30/0.75. Form elongate, narrow, transversely convex, especially elytra. Color black, dorsum strongly punctate, interpunctal surfaces strongly shining.

Head shiny, frons moderately densely punctate, very sparsely pubescent; interocular foveae deep; interocular tuberculi distinct; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5 apical width, moderately densely punctate; pubescence very sparse on disc, more developed laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum length:width 5:14, anterior margin arcuate, without 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 straight in midregion; each lateral depression with posterior angle acute, lateral margin emarginate before posterior angle, with fringe of short setae; lateral fossulae shiny, deep, finely sparsely punctate; pronotal disc moderately convex, reliefs shiny, densely moderately coarsely punctate, each puncture with a recumbent seta; punctures absent between anterior and posterior foveae; median groove deep, moderately wide, extending nearly to margins, tapering at ends; anterior foveae oval, each separated from posterior fovea by about length of anterior fovea; posterior foveae oblique, deep, 1/2 as long as and twice as wide as median groove; posterolateral angles lacking impressions.

Elytra nearly parallel­sided in anterior 0.5, transversely convex on disc, with six rows of punctures in shallow striae between suture and humeri; punctures round, small, serially separated from each other by less than puncture width, each with a recumbent seta; intervals shiny, weakly rounded, width 1.5–2.0x that of punctures; posterior declivity gradual, summit slightly behind midlength; striae 2 and 3 terminating into 4 at about apical 0.15; elytral explanate margin very narrow, without distinct fringe of setae.

Metasternal glabrous area slightly longer than wide, suboval, shining. Abdominal ventrites 1–3 and basal part of 4 with hydrofuge pubescence.

Aedeagus ( Fig. 18 ): Length of main­piece 0.31 mm, length to tip of parameres 0.35 mm; lobes very long, in ventral aspect apically blunt with lateral angles pointed, not barbed; ventral notch U­shaped, narrowing slightly apically, dorsal notch U­shaped, not as deep as ventral notch; duct roundly expanded at tip which is subequal width of lobes; paramere tips slightly angulate on medial surface; apical paramere seta elongate, ca. 2x length of next longest seta, both of which are relatively thickened.

Females unknown.

Etymology. Named in reference to the body form.

Distribution. Currently known only from the type locality, Cygnet River, Kangaroo Island, South Australia (Fig. 93).

Figures

FIGURE 17. Gymnochthebius semicylindrus, holotype. Dorsal and lateral habitus.

FIGURE 18. Gymnochthebius semicylindrus. Aedeagus of holotype.