Hydraena billi 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 : 43

Hydraena billi Zwick, 1977

( Figs. 59 , 61, 63 , 262)

Hydraena billi Zwick, 1977: 165 .

Type Material. Holotype (male): Victoria, Delatite River below Sawmill Settlement [labels: Australia, Vic., Delatite R., 27.iv.1972 Hynes // Hydraena billi Zwick Holo-Typus des. P. Zwick 1977 // HOLOTYPE T- 13132 Hydraena billi Zwick, 1977 // DIGITAL IMAGE captured 2004 P. D. Perkins]. Deposited in the MVMA.

Differential Diagnosis. A very distinctive, flightless species with fused elytra ( Fig. 59 ); differentiated from other members of the billi Group by the oval elytra with reduced humeri and reduced number of punctures, the distinctively arcuate profile, and the very small, carinate plaques that are located in a non-hydrofuge, smooth depression that occupies all of the metaventral disc. The aedeagus ( Figs. 61, 63 ) is also quite distinct.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.46/0.63; head 0.19/ 0.35; pronotum 0.38/0.49, PA 0.38, PB 0.37; elytra 0.90/0.63. Frons and elytra dark brown, pronotum light brown, labrum, legs and maxillary palpi yellowish (but see notes). Wings absent; eyes small; body distinctively arcuate in profile; elytra strongly oval, peaked slightly at suture; humeri weak, explanate margin rather wide and thick; each elytron with only 9 or 10 series of punctures.

Frons punctures ca. 0.5–1xef; interstices shining, 0.5–6xpd. Clypeus microreticulate laterally, finely sparsely punctate medially. Mentum shining, very finely sparsely punctate; postmentum microreticulate. Genae raised, lacking posterior ridge. Pronotal disc slightly raised, punctures on disc extremely fine and sparse, ca. 1xpd smallest on frons, interstices shining; punctures much larger and denser at posterior; PF1 absent; PF2 very shallow; PF3 moderately deep, broad; PF4 shallow; area between PF3 and PF4 weakly convex.

Elytral punctures largest on basal 0.3, forming five or six irregular rows of varying length, punctures becoming finer and sparser posteriorly. Intervals shining, width on basal 1/3 ca. 2–3xpd. Apices in dorsal aspect conjointly rounded, in posterior aspect margins form marked angle with one another. Elytral epipleuron wide.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/0.1/1/2. P1 with median carina posterior extreme slightly more elevated than remainder. P2 moderately wide, l/w ca. 4/3, sides parallel, apex blunt. Plaques very small carinae located in non-hydrofuge, smooth depression that occupies all of metaventral disc. AIS flat, width at straight posterior margin 2x P2. Protibia gradually widened to midlength, then markedly excavate, a prominent tooth bearing a spine at base of excavation. Meso- and metatibia slender. Last sternite symmetrical or nearly so; last tergite with shallow, apicomedian emargination.

Aedeagus ( Figs. 61, 63 ) main-piece elongate, with small process on right side at distal extreme; distal piece with three lobes, the most median angled from right to left and terminating in small fimbriate part; left paramere large, medially displaced, with row of setae along ventral margin; right paramere very small lobe at distal extreme of main-piece, with long setae. Female last tergite with very small apicomedian incision, setae slender, tapering.

Distribution. Currently known from a comparatively tight cluster of localities in Victoria (Fig. 262).

Remarks. The male specimen from Myrtle Creek is almost uniformly dark brown.

Material Examined (8): Victoria, Cumberland Sc. Res. (sw Camberville), Cora Lynn Falls, Eucalyptus regnans / Nothofagus cunninghamii , wet leaves & flood debris, forest stream, FMHD #87-258, elev. 880 m, 37° 34' S, 145° 53' E, 5 February 1987, A. Newton & M. Thayer (1 FMNH); Myrtle Creek, NW Ben Cairn (NW Warburton), wet scleroph./ Nothofagus cunninghamii , wet leaves and flood debris, forest stream, FMHD 87-254, elev. 780 m, 37° 42' S, 145° 37' E, 1 February 1987, A. Newton & M. Thayer (821) (1 FMNH); Tanjil R., E. Branch, 4 km SE Tanjil Bren, wet scleroph./ Nothofagus cunninghamii , wet leaves and flood debris, for- est stream, FMHD 87-263, elev. 490 m, 37° 50' S, 146° 12' E, 10 February 1987, A. Newton & M. Thayer (829) (1 FMNH); Warburton, Cement Creek, flood debris, forest stream, elev. 670 m, 37° 42' S, 145° 44' E, 10–17 January 1980, A. Newton & M. Thayer (3 USNM); Warburton, Cement Creek, wet leaves and flood debris, forest stream, Eucalyptus regnans / Nothofagus cunninghamii, FMHD #87-225, elev. 670 m, 37° 43' S, 145° 42' E, 2 February 1987, A. Newton & M. Thayer (812) (1 FMNH); Wilk’s Creek on road from Melbourne to Marysville, 37° 32' S, 145° 44' E, 26 December 1971, Hynes (1 PZC).

Figures

FIGURES 57–60. Hydraena, dorsal and lateral habitus of holotypes. —57. H. hynesi. —58. H. monteithi. —59. H. billi. —60. H. biimpressa.

FIGURES 61–64. Hydraena, aedeagi of holotypes. —61. H. billi. —62. H. biimpressa. —63. H. billi (after Zwick 1977). —64. H. monteithi.