Hydraena tenuisella, 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 : 49-50

Hydraena tenuisella new species

(Figs. 74, 80, 261)

Type Material. Holotype (male): Queensland, 3 km W of Batavia Downs , 12° 40' S, 142° 39' E, Malaise Trap, 18 June–22 July 1992, P. Zborowski & E. S. Nielsen. Deposited in the ANIC.

Differential Diagnosis. Recognized from all species, except H. weiri and H. arcta , by the very flat, narrow, parallel-side form (Figs. 74, 75, 67). H. tenuisella is larger than both H. weiri and H. arcta (ca. 1.39, 1.25, 1.13 mm respectively); however, these species are very similar in dorsal sculpture and plaque proportions; reliably distinguishing among the three species will require examination of the aedeagi (Figs. 78–80).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.39/0.53; head 0.22/ 0.34; pronotum 0.34/0.41, PA 0.36, PB 0.37; elytra 0.82/0.53. Dorsum brown; legs and palpi light brown to testaceous, tip of last palpomere not darker (labrum and clypeus are lighter than frons, but this may due to teneral condition of holotype).

Frons punctures ca. 1xef; interstices shining, 1–3xpd. Clypeus microreticulate. Mentum weakly shining, very finely sparsely punctate; postmentum microreticulate. Genae weakly raised, lacking posterior ridge. Pronotum finely sparsely punctate on disc, more densely punctate anteriorly and posteriorly; punctures on disc ca. 1xpd those of frons, interstices strongly shining, 2–5xpd; punctures anteriorly and posteriorly ca. twice as large as those on disc, interstices 1–2xpd; PF1 and PF4 absent; PF2 very shallow, almost absent; PF3 very shallow, broad.

Elytral punctures ca. 1xpd of smallest pronotal punctures. Intervals not raised, strongly shining, width about 2–3xpd, as are interstices between punctures of a row. Elytra parallel-sided or nearly so. Apices in dorsal aspect truncate, in posterior aspect margins form marked angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 2/2/7/2. P1 laminate; median carina weakly angulate in profile. P2 l/w ca. 5/2, sides parallel or weakly diverging, apex blunt. Plaques large, slightly raised, located in posterior 3/5 of metaventrite on sides of shallow median depression; plaques straight, slightly converging anteriorly. AIS flat, width at arcuate posterior margin ca. 2x P2. Legs simple. Last tergite cap-like, with small apicomedian concavity.

Aedeagus (Fig. 80) main-piece with very large basal orifice; distal piece with two large lobes and three narrow processes, process that terminates in gonopore-bearing flagellum widened before flagellum; both parameres inserting at same level, near base of main-piece; left paramere very narrow, about same length as right, with about eight setae on ventral surface apically; right paramere enlarged basally, weakly arcuate, very sharply pointed, with about four long setae on ventral surface near proximal 1/3. Females not yet known.

Etymology. Named in reference to the narrow and thin body form.

Distribution. Currently known only from the type locality near Batavia Downs, in far northern Queensland (Fig. 261).