Gymnochthebius nanosetus, 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 nanosetus new species

(Figures 64, 65, 74)

Type Material. Holotype (male): Australia: Northern Territory: Roderick Creek, Gregory N.P., M. V. Light, Operation Raleigh 1986, 15° 38' S, 131° 22' E, 4–6 July 1986, I. Archibald. Deposited in the MAGD.

Differential Diagnosis. Recognized by the small size, the short and slightly thickened dorsal setae, the fringe of arcuate setae on the elytral lateral margins, and the microreticu­

late dorsum (Fig. 64). Similar to G. squamifer (Fig. 66) in having abdominal hydrofuge pubescence reduced to the first two ventrites, but differing in larger size, narrower dorsal setae, narrower fringe of setae on the elytra, smaller elytral punctures, discrete elytral intervals as wide as serial punctures, non­confluent anterior­posterior pronotal foveae, and abdominal hydrofuge restricted to the 1st ventrite and all of the 2nd except the apical edge. The male genitalia of the two species are quite distinct (Figs. 65, 67).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.41/ 0.63; head 0.22/0.41; pronotum 0.37/0.56; elytra 0.86/0.63. Form moderately ovate, convex. Color dark brown, dorsum weakly shining, with distinctive short whitish or yellowish setae.

Head with dorsum clothed in distinctive recumbent setae near eyes and laterally on frons; frons finely sparsely punctate; interocular foveae deep; interocular tuberculi distinct; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength about 0.5 apical width, finely sparsely punctate. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width three times length, anterior margin arcuate, with 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 arcuate between lateral depressions; each lateral depression with posterior angle slightly acute, lateral margin weakly arcuate, densely clothed in setae which overlap one another; lateral fossulae deep, terminating anteriorly in pit; pronotal disc moderately convex, very effacedly microreticulate and finely sparsely punctate, each puncture with a distinctive recumbent whitish seta which contrasts with dark cuticle; median groove moderately deep and wide, constricted in midlength, wider anteriorly than posteriorly, extending nearly to margins, tapering at ends; anterior foveae well developed, deep; posterior foveae oblique, linear impressions 1/2 as long as and about as wide as median groove; posterolateral angles lacking impressions.

Elytra quite convex on disc; six rows of non­striate impressed punctures between suture and humeri, punctures closely spaced and nearly as wide as intervals; each puncture with a distinctive short narrow flat decumbent seta; summit of declivity at midlength; sutural margin slightly raised; elytral explanate margin very narrow, with fringe of arcuate setae over anterior 0.5.

Metasternal glabrous area slightly wider than long, subrhomboidal. Abdominal ventrites 1 and all of 2 except apical edge with hydrofuge pubescence.

Aedeagus (Fig. 65): Length of main­piece 0.25 mm, parameres not extending beyond main­piece; lobes long, barbed well before apices which are slightly bent; notch narrowed slightly apically; apical paramere setae short, subequal in length.

Females unknown.

Etymology. Named in reference to the small size and setose dorsum.

Distribution. Currently known only from the type locality in Gregory National Park,

Northern Territory (Fig. 74).