Hydraena robusta Zwick, 1977

PERKINS, PHILIP D., 2007, A revision of the Australian species of the water beetle genus Hydraena Kugelann (Coleoptera: Hydraenidae), Zootaxa 1489 (1), pp. 1-207 : 64-65

Hydraena robusta Zwick, 1977

(Figs. 95, 97, 258)

Hydraena robusta Zwick, 1977: 158 .

Type Material. Holotype (male): Tasmania, Hobart [labels: Hobart Tas: Lea // Griffith Collection Id. by A. M. Lea // 14622 Hydraena Tasmania. // Hydraena robusta Zwick male Holotypus // DIGITAL IMAGE captured 2004 P. D. Perkins]. Deposited in the SAMA.

Differential Diagnosis. Differentiated from other large species (ca. 2.25 mm), by the relatively large size of the pronotum, its wide shape and distinctly concave anterior margin, the narrow, elongate, and widely spaced plaques, and, in males, the form and setae of the metatibiae (Fig. 97). The metatibiae of males are weakly arcuate, weakly and gradually widened from base to apex, and the inner surface bears a brush of stiff setae over the distal 2/5. The aedeagus (Fig. 95) is quite distinct.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.06/0.89; head 0.28/ 0.48; pronotum 0.40/0.72, PA 0.56, PB 0.62; elytra 1.27/0.89. Dorsum dark brown, head slightly darker, margins of pronotum slightly lighter, legs and palpi light brown, distal 1/2 of last palpomere darker. Pronotum very transverse, anterior margin concave, side straight in front of and behind widest part.

Frons punctures ca. 2–3xef; interstices very narrow near eyes, 1–2xpd medially. Clypeus microreticulate laterally, finely sparsely punctate medially. Mentum shining, very finely sparsely punctate; postmentum microreticulate. Genae raised, lacking posterior ridge. Pronotum densely coarsely punctate, punctures on disc deep, ca. 3xpd those of frons, interstices 1–3xpd on middle of disc, slightly denser anteriorly and posteriorly; PF1 indicated by dense punctation; PF2 and PF4 shallow; PF3 moderately deep.

Elytral punctures about equal size of largest pronotal punctures. Intervals narrow, not raised, width about 0.5–1xpd, as are interstices between punctures of a row; a few extra punctures near scutellum. Apices in dorsal aspect conjointly rounded, in posterior aspect margins forming angle with one another.

Plaque/intercoxal process ratios (P2/w/l/s) ca. 1/1/5/3. P1 laminate; median carina angulate in profile. P2 moderately narrow, l/w ca. 5/1, sides parallel or slightly converging toward blunt apex. Plaques parallel or slightly convergent anteriorly, located in posterior 7/10 of metaventrite on sides of deep median elongate depression. No midlongitudinal carina between mesoventral intercoxal process and plaques. AIS flat, width at arcuate posterior margin 3x P2. Protibia thickened on inner surface near distal 3/4. Mesotibia slender. Metatibia weakly arcuate, inner surface with brush of stiff setae over distal 4/10. Abdominal apex setose, with depression on ventral face of last tergite.

Aedeagus (Fig. 95) main-piece with very large, arrow-shaped process apically; distal piece moderately complicated, with short gonopore bearing flagellum; left paramere shorter than right and inserted more distally on main-piece; right paramere very slender, setae in one group at weakly widened apex. Female last tergite without incisions; setae stout, forming a row, tips blunt and angled ventrad.

Distribution. Currently known from Victoria and Tasmania, and one disjunct locality in southern Queensland (Fig. 258).

Remarks. Some specimens have the pronotal discal punctures denser than the holotype. Females generally have the metaventral depression narrower than that of males.

Material Examined (47): Queensland, Girraween N. P., Bald Rock Creek at "Under-ground Creek", ex. sand/gravel streambank , 28° 51' S, 151° 57' E, 22 January 1998, P. D. Perkins (5 MCZ) ; Tasmania, Derby, 41° 9' S, 147° 49' E, 1 January–30 December 1960, C. Watts (1 SAMA) ; Mount, creek Barrow, inundation debris, 41° 22' S, 147° 21' E, 8 December 1982, Endrödy-Younga (AU 101) (7 TMSA) ; Nile River , 5 km NE of Deddington, cobble-bank of small river; remnant sclerophyll forest, pasture, elev. 275 m , 41° 34' S, 147° 28' E, 17 February 2000, N. Porch (72) (3 ANIC) ; St. Patric River , Targa, inundation debris , 41° 18' S, 147° 21' E, 8 December 1982, Endrödy-Younga (AU 104) (3 TMSA) ; Victoria, 10 km NE Mirranatwa , small creek bed/drying pool, stony, dead leaves, dry sclerophyll forest , 37° 36' S, 142° 13' E, 12 October 1997, C. Watts (10 SAMA) ; Base of Trentham Falls , 2.3 km N Trentham, amongst wet gravel at edge of waterfall splash pool and outlet. Dry sclerophyll forest [creek], elev. 640 m , 37° 22' S, 144° 19' E, 31 January 1999, N. Porch (NP 23) (1 ANIC) ; Fryer’s Creek near mouth into Lake Eildon , 37° 11' S, 145° 53' E, 3 October 1972, P. Zwick (1 PZC) ; Jamieson River at Jamieson , 38° 35' S, 143° 53' E, 2 October 1972, P. Zwick (1 PZC) ; Kangaroo Creek on Springhill Rd. , 5.8 km E Glenlyon, amongst weeds in shallow water at edge of creek (perennial) pools, dry sclerophyll forest, elev. 510 m , 37° 18' S, 144° 18' E, 31 January 1999, N. Porch (NP 24a) (1 ANIC) ; Mt. Buffalo N. P., The Cathedral, Leviathan, elev. 1550 m, 36° 44' S, 146° 46' E, 14 February 1998, L. Hendrich (11 NMW) ; Woori Yallock Creek east of Melbourne , on road to Warburton , 37° 44' S, 145° 29' E, 10 November 1972, P. Zwick (1 NMW, 2 PZC) .