Hydraena nanopala, 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 : 115-116

Hydraena nanopala , new species

( Figs. 206 , 208, 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 (50 NMW) .

Differential Diagnosis. Similar in general dorsal sculpture and pronotal shape to H. maculopala ( Figs. 203 , 206 ); differing therefrom by the smaller size (ca. 1.23 vs. 1.32 mm), the lack of a pronotal macula, the broader body with proportionally shorter elytra (PW/EL ca. 0.63 vs. 0.58), and the slightly more narrowly separated plaques (ratios ca. 4/1/5/4 vs. 4/1/5/5). Among Pala group members, the mesoventral intercoxal process (P2) is the narrowest in these two species. They also show a similarity in basic aedeagal plan, while differing distinctively in details of the distal piece ( Figs. 205 , 208); reliable determinations will require examination of the aedeagi.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.23/0.58; head 0.21/0.32; pronotum 0.31/0.46, PA 0.35, PB 0.37; elytra 0.73/0.58. Dorsum with frons piceous, remainder of dorsum dark reddish brown, disc of pronotum slightly darker than surrounding area; legs light brown to light reddish brown; maxillary palpi testaceous, tip not darker.

Frons punctures ca. 1xef, slightly larger near eyes than medially; interstices shining, 1–4xpd. Clypeus microreticulate laterally, very finely sparsely punctate medially. Mentum very sparsely very finely punctulate, shining; postmentum medially micropunctulate, otherwise finely sparsely punctulate. Genae raised, shining, without posterior ridge. Pronotum subcordiform, ca. median 3/4 of anterior margin arcuate to posterior; punctures on disc ca. 1xpd frons punctures, interstices shining, 1–3xpd, punctures slightly larger and denser at anterior and posterior; PF1 very shallow, obsolete; PF2 very shallow; PF3 moderately deep; PF4 absent or very shallow.

Elytra with summit of posterior declivity at or very near midlength; lateral explanate margins moderately 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. 1–3xpd, as are interstices between punctures of a row. Apices in dorsal aspect conjointly rounded, in posterior aspect margins forming shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 4/1/5/4. P1 ca. 2.5/4 P2; median carina straight in profile; postcoxal process medially concave. P2 transversely slightly concave, l/w ca. 3/5, sides slightly diverging toward blunt apex. Plaques very narrow, carinate, converging slightly anteriorly, at sides of median depression. Metaventrite concave between P2 and plaques. AIS width at straight posterior margin ca. 1.5x 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, medial margin flat in distal 1/4. Meso- and metatibia straight. Abdominal apex symmetrical; last tergite (male) deeply notched. Aedeagus as illustrated ( Fig. 208).

Etymology. Named in reference to the small size; the smallest member of the Pala group.

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

Figures

FIGURE 203. Hydraena maculopala, holotype, dorsal and lateral habitus, and venter.

FIGURE 206. Hydraena nanopala, holotype, dorsal and lateral habitus, and venter.

FIGURES 527–530. Geographical distributions of Hydraena species.

FIGURES 204–205. Aedeagi of holotypes. 204. H. pala. 205. H. maculopala.