Gymnochthebius nicki, 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 nicki new species

(Figures 31, 32, 81, 94–97)

Type Material. Holotype (male): Australia: Victoria: Possum Hollow falls, W. br. Tarwin River , 5.6 km SSW Allambee, ex sandy mud between cobbles at edge of riffle 0.1 km below waterfall; wet sclerophyll forest ( Eucalyptus regnans ), elev. 240 m, 38° 19' S, 146° 1' E, 14 January 1999, N. Porch (NP 18). Deposited in the ANIC . Paratypes (108): Australia: Victoria: 1 km N Possum Hollow, W. br. Tarwin River , 4.6 km SSW Allambee , ex shaded silty mud at edge of small 'creek' at pasture­wet sclerophyll forest boundary, elev. 240 m, 38° 18' S, 146° 1' E, 14 January 1999, N. Porch (NP 19) (56 ANIC); Bunyip R. at Princes Highway, amongst willow roots and on sand at edge of river under thick wil­

low cover in pasture, elev. 40 m, 38° 5' S, 145° 45' E, 15 January 1999, N. Porch (NP 22) (1 ANIC) ; Diamond Ck. , 1.8 km NNE Tonimbuk, on fine­medium sand and amongst litter on sandbar in small creek flowing through dry sclerophyll forest, elev. 110 m, 37° 59' S, 145° 42' E, 4 February 1999, N. Porch (NP 25) (1 ANIC) ; Elizabeth Ck. , 1.2 km S Childers, very abundant in sandy mud and wet litter (80cm by 20cm) along edge of small forest creek in wet sclerophyll forest ( Eucalyptus regnans ), elev. 195 m, 38° 19' S, 146° 6' E, 28 October 1998, N. Porch (NP 09) (2 ANIC) ; Elizabeth Ck. , 1.5 km N Allambee South, mud at edge of creek flowing under shady willows, elev. 125 m, 38° 20' S, 146° 7' E, 11 September 1998, N. Porch (NP 05) (8 ANIC) ; Little Morwell River at Mirboo Nth ­ Morwell Rd., 3.75 km NNE Mirboo North, on and in shaded muddy sand at edge of 'small creek' in dry sclerophyll forest, elev. 165 m, 38° 22' S, 146° 11' E, 14 October 1998, N. Porch (NP 08) (2 ANIC) ; Morwell River on Boolarra­Morwell Rd. , S43, LaTrobe C. Survey, river, 38° 19' S, 146° 19' E, 5 December 1978, [collr. not given] (3 MVMA) ; Possum Hollow falls , W. br. Tarwin River, 5.6 km SSW Allambee, ex sandy mud between cobbles at edge of riffle 0.1 km below waterfall; wet sclerophyll forest ( Eucalyptus regnans ), elev. 240 m, 38° 19' S, 146° 1' E, 14 January 1999, N. Porch (NP 18) (8 ANIC) ; Yarra River at Launching Place, margin of Yarra River on silty fine sand, elev. 115 m, 37° 47' S, 145° 35' E, 23 February 1999, N. Porch (NP 36) (27 ANIC) . Representative specimens to be deposited in BMNH, CMNH, FMNH, MCZ, MVMA, NMW, NPC, and QMBA .

Differential Diagnosis. Recognized by the very convex dorsum, the cuticular transparency, the arcuate anterior pronotal margin, the shining, very finely sparsely punctate pronotal reliefs, the strongly punctate elytra, and the distinctive fringe of long but rather sparse setae on the elytral margin (Fig. 31). Distinguished from G. trilineatus , which is also quite convex dorsally, by the non­confluent pronotal foveae. The male genitalia of the two species show some similarity, both lacking barbs, but in G. nicki the parameres are shorter, the lobes more rounded, the notch shallower, and the main­piece subapically wider (Figs. 30, 32).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.79/ 0.78; head 0.33/0.48; pronotum 0.41/0.63; elytra 1.11/0.78. Form moderately ovate, convex, especially transversely convex on elytra. Color brown with some transparency, head dark brown or piceous, dorsal surface shiny, non­microreticulate.

Head shiny, frons very finely sparsely punctate, sparsely pubescent; interocular foveae deep, pubescent; interocular tuberculi indistinct; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength 0.5 apical width, very sparsely punctate; pubescence very sparse on disc, slightly more developed laterally. Labroclypeal suture straight in dorsal view, evenly arcuate in anterior view. Labrum width:length as 7:2, anterior margin broadly and shallowly emarginate, apicomedially raised in form of very small tooth (male only).

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 slightly produced in midregion; each lateral depression with posterior angle produced to form small point, lateral margin setose, weakly arcuate; lateral fossulae shiny, deep, lacking microsculpture; pronotal disc transversely convex, shiny, extremely finely sparsely punctate, each puncture with a recumbent seta; median groove deep, moderately wide, extending nearly to margins, tapering at ends; anterior foveae oval, each separated from posterior fovea by 1–2 times length of anterior fovea; posterior foveae oblique, deep, linear impressions 1/2 as long as and as wide as median groove; posterolateral angles lacking impressions.

Elytra very convex on disc, with six rows of punctures in moderately well developed striae between suture and humeri; intervals shiny, rounded, width slightly greater than that of punctures, with sparse erect setae, especially behind elytra midlength; punctures round, separated from each other by about puncture width, each with a recumbent seta; summit of declivity at or slightly in front of midlength; sides of elytra nearly vertical in posterior 1/4, apices conjointly sharply rounded; striae 2 and 3 terminating into 4 at about apical 1/4; elytral explanate margin very narrow, with distinctive fringe of long but rather sparse setae.

Metasternal glabrous area length equal width, suboval, shining, slightly convex. Abdominal ventrites 1–3 and basally 4 with hydrofuge pubescence.

Aedeagus (Fig. 32): Length of main­piece 0.31 mm, length to tip of parameres 0.34 mm; lobes moderately long, slightly widened apically, not barbed; notch U­shaped, widest apically; apical paramere seta ca. 2x length of other longer setae.

Females are similar to males in form of the elytral explanate margin; the labrum is apicomedially emarginate.

Etymology. Named in honor of the collector, Nicholas Porch.

Distribution. Currently known from southern Victoria (Fig. 81).