Gymnochthebius lustrosulcus, 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 lustrosulcus new species

(Figures 27, 28, 73)

Type Material. Holotype (male): Australia: Queensland: Cloncurry , 20° 42' S, 140° 30' E, 29 April 1963, C. Watts. Deposited in the SAMA . Paratypes (158): Australia: New South Wales: Darling River , shore washing, 23° 11' S, 141° 42' E, 1 October 1982, Endrödy­Younga (AU­24) [labels read Darling River, but based on geocodes this would be the Diamantinna River] (78 TMSA) ; Fowlers Gap , shore washing, 30° 55' S, 141° 36' E, 3 October 1982, Endrödy­Younga (AU­25) (40 TMSA) ; Gilgandra , 31° 42' S, 148° 40' E, 19 November 1992, C. Watts (1 SAMA) ; Queensland: Boulia , 22° 54' S, 139° 54' E, 1–30 July 1972, C. Watts (2 SAMA) ; Carnarvon Ck. 17 km E Park Office, 25° 1' S, 148° 18' E, 14 August 2004, A. Glaister (1 NMW) ; Cloncurry , 20° 42' S, 140° 30' E, 29 April 1963, C. Watts (18 SAMA) ; Julia Creek , creek, 20° 3' S, 141° 12' E, 24 April 1963, C. Watts (6 SAMA) ; Queensland [no other data], 1 January 1917 – 30 December 1918 (1 NMW) ; Richmond , 20° 56' S, 143° 20' E, 1 October 1917 (1 NMW) ; same locality, 1 December 1917 (1 NMW) ; same locality, 1 March 1918 (3 NMW) ; same locality, 12 March 1918 (2 NMW) ; same locality, 4 May 1918 (2 NMW) ; South Australia: Tatiara Ck North of Bordertown , 36° 17' S, 140° 48' E, 22 February 1994, Aust. water quality centre 3064 (1 SAMA) ; Warburton R., 1 km N White Bull Yard Kalamurina Stn., 27° 52' S, 137° 54' E, 6 October 1999, WHC exped. (1 SAMA) . Representative specimens to be deposited in ANIC, BMNH, CMNH, FMNH, MCZ, MVMA, NPC, QMBA, QPIM, USNM, and WAMP .

Differential Diagnosis. A highly shining species recognized by the pronotum with distinct median groove and lacking posterior foveae, the markedly striate­impressed elytral series, and the large, rhomboidal metasternal glabrous area. Distinguished from G. radiatus , the only other species lacking posterior pronotal foveae, by the distinct pronotal median groove, the smaller lateral depressions of the pronotum, and the more deeply impressed elytral striae. Both species have the abdominal hydrofuge pubescence reduced to lateral areas of the first and second ventrites. The male genitalia of the two species bear some resemblance, but differ in several details, including shapes of the lobes and duct (Fig. 26, 28).

Description. Size (length/width, mm) holotype: body (length to elytral apices) l.60/ 0.75; head 0.30/0.44; pronotum 0.37/0.59; elytra 1.11/0.75. Form moderately ovate, convex, especially transversely convex on elytra. Color brown to dark brown, dorsal surface very shiny, non­microreticulate.

Head shiny, frons very finely sparsely punctate; interocular foveae deep, transverse; interocular tuberculi distinct, transverse; basomedial fovea narrowly confluent with interocular foveae. Frontoclypeal suture deeply impressed, bisinuate. Clypeus midlength equal apical width, very sparsely punctate. Labroclypeal suture weakly bisinuate in dorsal view, evenly arcuate in anterior view. Labrum width twice length, anterior margin arcuate, apicomedially raised in form of very small tooth (both sexes).

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 weakly bisinuate; each lateral depression weakly convex, with posterior angle obtuse, not markedly produced to form small point, lateral margin densely setose, weakly arcuate; lateral fossulae shiny, moderately deep, lacking microsculpture, terminating anteriorly in a small pit; pronotal disc transversely convex, very shiny, extremely finely sparsely punctate, almost glabrous, each puncture with a minute recumbent seta; median groove moderately deep, very narrowly incised, highlighted by brightly shining cuticle at edges, extending nearly to margins, tapering at ends; anterior foveae very small, pit­like; posterior foveae absent; posterolateral angles lacking impressions.

Elytra very transversely convex on disc, with six rows of punctures in moderately well developed striae between suture and humeri; intervals shiny, rounded, width 2–3 times that of punctures; punctures very small, slightly elongate, separated from each other by about puncture length, lacking discernible setae; summit of declivity at or slightly in front of midlength; sides of elytra nearly vertical in posterior 1/4, apices separately rounded; striae 2 and 3 terminating into 4 at about apical 1/4; elytral explanate margin very narrow, with distinctive fringe of short setae.

Metasternal glabrous area length less than width (as 16:22), subrhomboidal, anteriorly nearly attaining intercoxal process, shining, convex. Abdominal ventrites 1–2 laterally with hydrofuge pubescence, absent in midline; perhaps minutely present basolaterally on 3.

Aedeagus (Fig. 28): Length of main­piece 0.31 mm, parameres attaining same level; lobes relatively long, weakly barbed subapically; notch nearly parallel sided; duct relatively large; apical paramere seta short.

Females have the elytral explanate margin similar to that of males; the labrum has an apicomedian tooth, smaller than that of males.

Etymology. Named in reference to the very lustrous pronotal disc, which highlights the median sulcus.

Distribution. Currently known from eastern Queensland south to southeastern South

Australia, and one locality in New South Wales (Fig. 73).