Hydraena apexa, 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 : 123-124

Hydraena apexa , new species

( Figs. 226 , 228, 535 )

Type Material. Holotype (male): Eastern Highlands Province: Okapa , under wet leaves left by receding pond, 1524 m, 6° 32' S, 145° 37' E, 10 ii 1965, M. E. Bacchus (MEB 190) ( NHM) . Paratypes: Eastern Highlands Province: Aiyura , 1670 m, 6° 21.131' S, 145° 54.398' E, 5 iv 2006, Balke & Sagata ( PNG 32) (57 MCZ, NHM, NMW, PNG, ZSM) .

Differential Diagnosis. Recognized among members of the Ulna group ( Figs. 222 , 223 , 226 ) by the comparatively large size (ca. 1.85 vs. 1.46 and 1.57 mm), the rather wide pronotum that is emarginate between the anterior angle and widest point, and the comparatively large metaventral plaques (plaque ratios ca. 4/3/10/5). Males additionally recognized by the arcuate metatibiae, and the markedly asymmetrical abdominal apex. The male genitalia distinctively differ from those of the other two species in the Ulna group ( Fig. 228).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.85/0.81; head 0.26/0.41; pronotum 0.46/0.64, PA 0.47, PB 0.53; elytra 1.13/0.81. Dorsum of head dark brown to piceous; pronotum dark brown around piceous, very diffusely margined, rectangular macula, ratios of color bands, as measured in midline, ca. 8/18/5; elytra dark brown; legs brown; maxillary palpi testaceous, tip not darker. Dorsum moderately shining.

Frons punctures ca. 1xef near eyes, smaller and sparser medially; interstices 1–4xpd, laterally microreticulate, dull, medially shining. Clypeus effacedly microreticulate laterally, very finely sparsely punctulate and shining medially. Mentum effacedly microreticulate, very sparsely very finely punctulate, weakly shining. Postmentum microreticulate in shallow median depression, otherwise finely sparsely punctate. Genae very slightly raised, shining, with shallow, obsolete median impression, without posterior ridge. Pronotum transverse, anterior margin straight, sides slightly emarginate between anterior angle and widest part, arcuate at middle, sinuate between widest part and posterior angle; punctures on disc ca. 2–3xpd largest frons punctures, interstices shining, ca. 1–3xpd, punctures anteriorly and posteriorly ca. 3–4xpd those on disc; PF1 and PF2 very shallow; PF3 moderately deep, wide; PF4 absent.

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

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 4/3/10/5. P1 laminate; median carina sinuate in profile, slightly raised behind coxae. P2 length/width ca. 7/4, sides parallel, apex blunt, slightly raised. Plaques large, flat or slightly raised, widest at midlength, at sloping sides of median depression, anteriorly tapering and convergent, narrowly separated at anterior extreme. Metaventrite between mesocoxae very weakly raised in midline. AIS width at straight posterior margin slightly less than 2x P2. All legs of moderate length. Profemur (male) with minute tubercle on ventral margin near trochanter; protibia very slightly arcuate, medial margin slightly emarginate and concave, except distal 1/4 widened, posteromedial margin of concavity with row of short spines. Mesotibia straight, slender. Metatibia slender, slightly arcuate, distal 1/2 of medial margin with brush of setae. Abdominal apex markedly asymmetrical; last tergite (male) with large notch, offset to right side. Aedeagus as illustrated ( Fig. 228).

Etymology. Named in reference to the pointed processes of the aedeagus, and to the relatively long apical area of the pronotum.

Distribution. Currently known from two localities in eastern Area 1; elevations 1524 m and 1670 m ( Fig. 535 ).

Figures

FIGURE 222. Hydraena ulna, holotype, dorsal and lateral habitus, and venter.

FIGURE 223. Hydraena pectenata, holotype, dorsal and lateral habitus, and venter.

FIGURE 226. Hydraena apexa, holotype, dorsal and lateral habitus, and venter.

FIGURES 535–538. Geographical distributions of Hydraena species.