Hydraena trapezoidalis 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 : 115-116

Hydraena trapezoidalis Zwick, 1977

(Figs. 195–197, 247)

Hydraena trapezoidalis Zwick, 1977: 178 .

Type Material. Holotype (male): Northern Territory, Howard Springs , 24 km S of Darwin [ca. 12° 28' S, 131° 3' E] [labels: 12.28S 131.03E // Howard Springs, N. T., 24 km S of Darwin 10.xi.72, rainforest, at light, E. Britton // [pink label] // Holotype // Aedeagus drawn by P. D. Perkins // DIGITAL IMAGE captured 2004 P. D. Perkins // Hydraena trapezoidalis Zwick Holo-Typus des. P. Zwick 1977]. Deposited in the ANIC.

Differential Diagnosis. Recognized from other members of the trapezoidalis Group by the combination of small size (ca. 1.19 mm), the shorter, less widely separated plaques, and the fasciate pronotum. Differs additionally from H. ruinosa by the shorter elytra with more broadly rounded apices, and from H. fundata by the thicker metatibiae (Figs 192, 193, 195). The aedeagus is distinctive (Figs. 196, 197).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.19/0.54; head 0.20/ 0.31; pronotum 0.32/0.43, PA 0.31, PB 0.43; elytra 0.73/0.54. Head piceous; pronotum with large dark brown to piceous fascia, bordered narrowly anteriorly and posteriorly by testaceous; elytra dark brown; maxillary palpi and legs testaceous. Dorsum strongly shining.

Frons punctures near eyes slightly less than 1xef, much finer and very sparse on disc. Clypeus very finely sparsely punctate on disc, very weakly, effacedly microreticulate laterally. Mentum shining, very finely sparsely punctate; postmentum finely punctate. Genae raised, lacking posterior ridge. Pronotum very finely, very sparsely punctate; PF1, PF2 and PF4 absent; PF3 shallow, broad.

Elytral punctures very fine and very sparse, becoming obsolete over posterior declivity. Intervals not raised, strongly shining. Apices in dorsal aspect conjointy rounded, in posterior aspect margins form moderately strong angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 4/2/6/2. P1 slightly wider than laminate; median carina straight in profile. P2 weakly concave, moderately wide, l/w ca. 5/3, sides parallel or slightly divergent, apex blunt. Plaques large, convergent and nearly confluent anteriorly, located on sides of moderately deep median triangular depression. AIS flat, width at arcuate posterior margin less than 2x P2. Protibia weakly arcuate, gradually increasing in width from base to apex. Mesotibia and metatibia slender, simple. Last sternite symmetrical or nearly so; last tergite with small apicomedian notch.

Aedeagus (Figs. 196, 197) main-piece distally extending in process that carries short gonopore bearing flagellum; distal piece with bilobed process on left side, rounded process with hair-like bristles on right side, behind which is striated lobe, visible in lateral view; left paramere longer than right, setae at apex and continuing along ventral margin; right paramere with setae at rounded apex. Female last tergite with three incisions, delimiting four lobes, setae on disc slender, tapering, setae along margin slender, tips blunt and bent ventrad, not forming a discrete line of setae as in the luridipennis Group.

Distribution. Currently known from northern Northern Territory, plus one locality in the 'center' and two closely spaced localities in northwestern Queensland (Fig. 247).

Remarks. Upon study of the holotype and paratype, I found that the undissected female (i.e., the paratype) was mounted on the pin with the holotype label and the male genitalia mount, whereas the dissected male (i.e., the holotype) was mounted on the pin with the paratype labels. I have switched the specimens, so they are with the proper labels. The male genitalia is in water soluble glue on the card with the holotype.

Material Examined (12): Northern Territory, 10 mi E of Daly River, at light, 13° 45' S, 130° 51' E, 28 June 1972, B. K. Head (1 SAMA); Howard Springs, 24 km S of Darwin, rain forest, at light, 12° 28' S, 131° 3' E, 10 November 1972, E. Britton (1 ANIC); Kakadu N. P., Gungurul Lookout, creek, elev. 50 m, 13° 59' S, 132° 19' E, 1 November 1996, L. Hendrich (7 NMW); Serpentine Gorge, West Macdonnells N. P., permanent rocky pools, sandy bottom, overhanging and floating vegetation, 23° 44' S, 132° 59' E, 8 March 1995, T . Weir (1 ANIC) ; Queensland, Murrays Spring, 8 km W by N of Musselbrook Mining Camp , large pool in rocky creek bed, sandy bottom water lillies, Pandanus , algal growth, 18° 35' S, 138° 3' E, 9–20 May 1995, T . Weir (1 ANIC); Musselbrook Creek , 2 km S of Musselbrook Mining Camp, large pool in rocky creek, sandy bottom, 18° 37' S, 138° 8' E, 9 May 1995, T . Weir (1 ANIC) .