Hydraena tritropis, 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 : 117-118

Hydraena tritropis , new species

( Figs. 211 , 213 , 528 )

Type Material. Holotype (male): Madang Province: Sepik Ramu Basin, Kojé Creek , unshaded creek, small to medium cobbles, gravel and fine sand (the latter in areas of slack water), filamentous algae on stony substrates, small accumulations of leaf litter, 160 m, 5° 33' S, 145° 23' E, 1 vii–30 viii 1988, D. Dudgeon ( NMW) . Paratypes: Same data as holotype (1 NMW) .

Differential Diagnosis. Differing from the other members of the Pala group by the shape of the prosternal median carina, which extends the entire length of the prosternum, is straight or very weakly arcuate in profile. Similar to H. torosopala in dorsal color and plaque ratios; differing therefrom by the smaller size (1.29 vs. 1.45 mm), the slightly broader form, and the prosternum differences ( Figs. 211 , 214 ). The male genitalia of the two species distinctively differ ( Figs. 213 , 216). Also see the diagnosis of H. koje .

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.29/0.61; head 0.21/0.32; pronotum 0.32/0.50, PA 0.36, PB 0.40; elytra 0.76/0.61. Dorsum with frons, clypeus, and elytra dark reddish brown; pronotum and legs brown to light brown; labrum and maxillary palpi testaceous, tip of palpus not darker.

Frons punctures ca. 1–2xef, larger and denser near eyes than medially; interstices shining, 1–3xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum and postmentum very sparsely very finely punctulate, shining. Genae raised, shining, without posterior ridge. Pronotum very transverse, ca. median 1/2 of anterior margin arcuate to posterior; punctures on disc ca. 1xpd of smallest frons punctures, interstices shining, 1– 2xpd, punctures not noticeably larger or denser at anterior and posterior; PF1 absent or very shallow; PF2 very shallow, obsolete; PF3 shallow; PF4 absent or very shallow.

Elytra with summit of posterior declivity at or very near midlength; lateral explanate margins rather wide; on basal 1/3 punctures ca. 1xpd largest pronotal punctures, a few punctures subserial, punctures becoming gradually smaller toward posterior. Intervals not raised, shining, on disc ca. 2–4xpd, as are interstices between punctures of a row. Apices in dorsal aspect slightly separately rounded, minutely denticulate, in posterior aspect margins forming shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 7/1/5/5. P1 ca. 6/7 P2; median carina extending for entire length of prosternum, straight or very weakly arcuate in profile. P2 transversely concave, l/w ca. 4/7, sides slightly diverging toward blunt apex. Plaques very narrow, carinate, converging slightly anteriorly, at sides of deep median depression. Metaventrite concave between P2 and plaques. AIS fused with first abdominal ventrite, width between metacoxae ca. 6/7 P2. All legs moderately long and slender. Profemur (male) without tubercle next to trochanter; protibia very slightly arcuate, gradually increasing in width from base to apex. Meso- and metatibia straight. Abdominal apex symmetrical; last tergite (male) deeply notched. Aedeagus as illustrated ( Fig. 213 ).

Etymology. "Three keels"; named in reference to the median longitudinal carina of the prosternum, and the two carinate plaques.

Distribution. Currently known only from the type locality, Kojé Creek, in the eastern arm of Area 3; elevation 160 m ( Fig. 528 ).

Figures

FIGURE 211. Hydraena tritropis, holotype, dorsal and lateral habitus, and venter.

FIGURE 214. Hydraena torosopala, holotype, dorsal and lateral habitus, and venter.

FIGURES 212–213. Aedeagi of holotypes. 212. H. formosopala. 213. H. tritropis.

FIGURES 527–530. Geographical distributions of Hydraena species.