Hydraena cygnus 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 : 91-92

Hydraena cygnus Zwick, 1977

(Figs. 147, 151, 152, 240)

Hydraena cygnus Zwick, 1977: 169 .

Type Material. Holotype (male): Western Australia, Swan River [labels: Swan R Lea // Griffith collection Id. by A. M. Lea // Hydraena cygnus Zwick male holotypus // DIGITAL IMAGE captured 2004 P. D. Perkins]. Deposited in the SAMA.

Differential Diagnosis. Externally very similar to other members of the ambiflagellata Group (Figs. 147–150); reliable determinations will require examination of the male genitalia (Figs. 151, 152).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.38/0.60; head 0.17/0.32; pronotum 0.36/0.47, PA 0.36, PB 0.46; elytra 0.84/0.60. Dorsum dark brown, anterior and posterior margins of pronotum slightly lighter, legs and maxillary palpi brown.

Frons punctures ca. 1xef; interstices shining, 0.5–3xpd. Clypeus microreticulate laterally, finely sparsely punctate medially. Mentum shining, very finely sparsely punctate; postmentum microreticulate. Genae raised, lacking posterior ridge. Pronotal punctures on disc ca. 1xpd those of frons, interstices shining, 2–4xpd, punctures denser at anterior, similar to frons; PF1 and PF4 absent; PF2 very shallow, nearly absent; PF3 shallow.

Elytral punctures about equal size of largest pronotal punctures. Intervals not raised, shining, width ca. 2xpd, as are interstices between punctures of a row. Apices in dorsal aspect gradually rounded, in posterior aspect margins form shallow angle with one another.

Plaque/intercoxal process ratios (P2/w/l/s) ca. 1/1/4/2. P1 laminate; median carina posterior extreme slightly more elevated than remainder. P2 narrow, l/w ca. 2/1, sides parallel, apex blunt. Plaques located in posterior 7/10 of metaventrite on sides of deep median subtriangular depression, plaques anteriorly very narrowly separated and lateral margins arcuate. Low midlongitudinal carina between mesoventral intercoxal process and plaques. Cuticle asperite under hydrofuge pubescence. AIS flat, width at arcuate posterior margin 2–3x P2. Protibia gradually widened to about distal 4/5, then markedly excavate, a prominent spine at base of excavation; metatibia with brush of setae on medial surface over distal 3/5. Last sternite symmetrical or nearly so; last tergite with small, slightly off-center concavity.

Aedeagus (Figs. 151, 152) main-piece extending as wide process on right side, as wide as distal piece, apex blunt; distal piece irregularly shaped, with an apical process visible in lateral view, gonopore flagellum very short, base of distal piece with large, striated lobe, visible in lateral view; left paramere wide, almost trilobed on margin, two small distal lobes each with two setae, ventral margin with row of long setae; right paramere about same length as left paramere, ventral margin curling around main-piece and bearing setae in two groups. Females not yet known.

Distribution. Currently known only from two localities in western Western Australia (Fig. 240).

Remarks. The aedeagus has the left paramere complete, not fused to the main-piece as illustrated by Zwick (1977).

Material Examined (4): Western Australia, Lake Nalyerin, 33° 8' S, 116° 22' E, 6 October 2002, C. H. S. Watts (3 SAMA); Swan River [no date], 31° 59' S, 115° 50' E ,, Lea (1 SAMA) .