Hydraena sexarcuata, Perkins, 2011

Perkins, Philip D., 2011, New species (130) of the hyperdiverse aquatic beetle genus Hydraena Kugelann from Papua New Guinea, and a preliminary analysis of areas of endemism (Coleoptera: Hydraenidae) 2944, Zootaxa 2944 (1), pp. 1-417 : 47-48

Hydraena sexarcuata , new species

( Figs. 63 , 65, 457 )

Type Material. Holotype (male): Eastern Highlands Province: Akameku–Brahmin , Bismarck Range, 700 m, 5° 52.754' S, 145° 23.209' E, 24 xi 2006, Balke & Kinibel ( PNG 109) ( ZSM) . Paratypes (19): Eastern Highlands Province: Same data as holotype (5 ZSM) ; Sandaun Province: Mianmin , pool, 990 m, 4° 54.57' S, 141° 35.49' E, 23 x 2008, S. Ibalim ( PNG 193) (1 ZSM) ; Mianmin , river, 700 m, 4° 52.858' S, 141° 31.706' E, 21 x 2008, S. Ibalim ( PNG 197) (1 ZSM) ; Mianmin , river,, 990 m, 4° 54.57' S, 141° 35.49' E, 23 x 2008, S. Ibalim ( PNG 192) (11 MCZ, NHM, NMW, PNG, ZSM) ; Mianmin , river,, 1080 m, 4° 55.78' S, 141° 38.185' E, 24 x 2008, S. Ibalim ( PNG 195) (1 ZSM) .

Differential Diagnosis. Differentiated from other members of the Otiarca group by the narrow, carinate plaques (plaque rations ca. 3/1/9/4) and, in males, the arcuate mesotibiae and the uniquely modified metatibiae ( Fig. 63 ). The male genitalia distinctly differ from other members of the Otiarca group, being more elongate and, in lateral view, less angulate ( Fig. 65).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.53/0.66; head 0.23/0.37; pronotum 0.38/0.47, PA 0.39, PB 0.41; elytra 0.92/0.66. Dorsum of head piceous; pronotum light brown to testaceous in front of and behind piceous fascia, ratios of color bands, as measured in midline, ca. 5/17/3; elytra dark brown; legs light brown; maxillary palpi testaceous, tip slightly darker.

Frons punctures ca. 1xef, slightly larger near eyes than medially; interstices shining, 1–3xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum very sparsely very finely punctulate, shining; postmentum effacedly micropunctulate. Genae raised, shining, without posterior ridge. Pronotum cordiform, median 1/2 of anterior margin emarginate; punctures on disc ca. 1–2xpd those of frons, interstices shining, 1–3xpd, punctures slightly larger and denser at anterior and posterior; PF1 absent; PF2 very shallow, obsolete; PF3 deep; PF4 absent.

Elytra with summit of posterior declivity slightly beyond midlength; lateral explanate margins moderately wide; on basal 1/3 punctures ca. 1xpd largest pronotal punctures, punctures becoming gradually smaller toward posterior. Intervals not raised, shining, on disc ca. 2–3xpd, as are interstices between punctures of a row, a few punctures subserial. Apices in dorsal aspect weakly separately rounded, in posterior aspect margins forming shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 3/1/9/4. P1 laminate; median carina sinuate in profile. P2 raised, l/w ca. 2/1, sides slightly converging toward blunt apex. Plaques very narrow, carinate, parallel, located at sides of deep median depression, each plaque tapering very slightly from posterior to anterior. Metaventrite without midlongitudinal ridge. AIS width at slightly arcuate posterior margin ca. 1.7x P2. All legs long and slender. Profemur (male) with small, sharply pointed tubercle next to trochanter; protibia slightly arcuate, widest subapically, anteromedial margin with cluster of small spines just before apex, moderately long spine on medial surface at ca. distal 1/3. Mesotibia slightly arcuate. Metatibia markedly arcuate, distal 1/3 widened and with medial margin bearing brush of hair-like setae. Abdominal apex symmetrical; last tergite (male) notched. Aedeagus as illustrated ( Fig. 65).

Etymology. Named in reference to the six arcuate tibiae of males.

Distribution. Currently known from the Mianmin area (700–1080 m), and one locality at Akameku–Brahmin (700 m); because of the combination of location and elevation these sites are considered to be in Area 2, although they border on Area 1 ( Fig. 457 ).

Figures

FIGURE 63. Hydraena sexarcuata, holotype, dorsal and lateral habitus, and venter.

FIGURES 455–458. Geographical distributions of Hydraena species.