Hydraena australula, Published, 2007

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 : 76

Hydraena australula new species

(Figs. 112, 116, 261)

Type Material. Holotype (male): Western Australia, Synnot Ck., CALM Site 25/1 [Western Australian Department of Conservation and Land Management], 16° 31' S, 125° 16' E, at light, closed forest margin, 17– 20 June 1988, T. A. Weir. Deposited in the ANIC . Paratype: Western Australia, Synnot Range , 16° 25' S, 125° 28' E, 1 September 1969, D. D. Giuliani (1 WAMP) .

Differential Diagnosis. Somewhat similar in dorsal habitus to H. australica and H. parciplumea ; differing therefrom by the much smaller size (ca. 1.08 vs. 1.45 and 1.31 mm), the slightly broader body form, the more sparsely punctate pronotum, the sparser, subserial or random elytral punctures, and the differently shaped plaques (Figs. 115–117). The aedeagus of H. australula shows some similarities with those of the compared species, but differs therefrom in the shape of the main-piece, the positions, shapes, and setal patterns of the parameres, and details of the main-piece (Figs. 112, 114, 119).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.08/0.49; head 0.16/ 0.29; pronotum 0.28/0.38, PA 0.30, PB 0.35; elytra 0.64/0.49. Head and elytra dark brown; pronotum brown; legs and palpi light brown to testaceous, tip of last palpomere not darker.

Frons punctures ca. 1xef; interstices shining, 2–5xpd. Clypeus microreticulate laterally, finely sparsely punctate and shining medially. Mentum weakly shining, very finely sparsely punctate; postmentum microreticulate. Genae weakly raised, lacking posterior ridge. Pronotal punctures on disc ca. 1xpd those of frons, slightly larger anteriorly and posteriorly, interstices shining, 2–5xpd, largest on disc; PF1 and PF4 absent; PF2 very shallow; PF3 shallow, broad.

Elytral punctures ca. 1xpd of smallest pronotal punctures, weakly serial, becoming random over posterior declivity. Intervals not raised, shining, width about 2–3xpd, as are interstices between punctures of a row. Elytral margins arcuate. Apices in dorsal aspect conjointly rounded, in posterior aspect margins do not form angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 2/1/7/3. P1 laminate; median carina weakly angulate in profile. P2 l/w ca. 2/1, sides parallel or weakly diverging, apex blunt. Plaques large, slightly raised, located in posterior 7/10 of metaventrite on sides of deep, subtriangular median depression; plaques weakly arcuate, tapering and narrowly separated anteriorly. AIS flat, width at arcuate posterior margin ca. 1.5x P2. Legs simple. Last tergite cap-like, with small apicomedian notch.

Aedeagus (Fig. 112) main-piece with very narrow, short, sinuate, pointed process on right side; distal piece with one lobe and two narrow processes in ventral view, multi-lobed in lateral view, with cluster of curving, long setae on dorsal surface, gonopore-bearing flagellum very short; both parameres inserting very near base; left paramere markedly sinuate in lateral view, longer than right, distal 1/2 slightly widened and with two groups of moderately long setae; right paramere weakly arcuate in lateral view, with about four setae on ventral margin near midlength. Females not yet known.

Etymology. Named in reference to the small size and relationship to H. australica .

Distribution. Currently known only from the Synnot Range in northeastern Western Australia (Fig. 261).