Hydraena tridisca, 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 : 120

Hydraena tridisca new species

(Figs. 83, 205, 256)

Type Material. Holotype (male): Queensland, Mt. Hemmant , elev. 1050 m, 16° 7' S, 145° 25' E, rainforest, sieved leaf litter & moss, QM berlesate No. 865, 27 November 1993, G. Monteith & H. Janetzki. Deposited in the QMBA.

Differential Diagnosis. An unusual species, recognized by the proportionally large and transverse pronotum, the very uniform pronotal punctation, the nearly parallel-sided body form (Fig. 205), and the very large, very narrowly separated plaques. The aedeagus is not easily compared to that of any other species (Fig. 83).

Description. Size (length/width, mm) holotype: body (length to elytral apices) 1.40/0.60; head 0.20/ 0.34; pronotum 0.35/0.50, PA 0.40, PB 0.43; elytra 0.85/0.60. Head dark brown to piceous; pronotum with dark brown macula surrounded by lighter brown; elytra dark brown; legs brown; maxillary palpi light brown, tip of last palpomere not darker.

Frons punctures ca. 1xef; interstices shining on disc, 1–2xpd, microreticulate laterally. Clypeus microreticulate and finely punctate. Mentum and postmentum weakly shining, microreticulate. Genae weakly raised, lacking posterior ridge. Pronotal punctures on disc ca. 2xpd those of frons, interstices shining, 1–2xpd, punctures slightly denser and slightly larger anteriorly and posteriorly; PF1 absent; PF2 very shallow, confluent forming U-shaped impression; PF3 moderately deep, broad; PF4 very shallow.

Elytral punctures ca. 1xpd of largest pronotal punctures. Intervals not raised, shining, ca. 1xpd, as are interstices between punctures of a row. Apices in dorsal aspect conjointly rounded, in posterior aspect margins form very shallow or no angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/4/9/0.8. P1 laminate; median carina weakly angulate in profile. P2 narrow, l/w ca. 3/1, sides parallel, apex blunt. Plaques very large, raised, separated by narrow groove; each plaque almost kidney-shaped, medial margin straight, lateral margin arcuate. AIS flat, width at arcuate posterior margin ca. 4x apex of P2. Protibia (male) arcuate, gradually increasing in width from base to apex; mesotibia and metatibia straight. Last tergite with apicomedian notch.

Aedeagus (Fig. 83) main-piece short compared with distal piece, with small process on ventral surface near base; distal piece disc-shaped, wider in lateral than ventral view, gonopore-bearing flagellum moderately long; parameres short, lobate, inserting near distal piece, with short setae; right paramere markedly bent. Females not yet known.

Etymology. Named in reference to the oval metaventral plaques and the disc-like shape of the aedeagus, as seen in lateral aspect.

Distribution. Currently known only from the type locality, Mt. Hemmant, in northeastern Queensland (Fig. 256).