Hydraena compacta, Perkins, 2017

Perkins, Philip D., 2017, Hydraenidae of Madagascar (Insecta: Coleoptera), Zootaxa 4342 (1), pp. 1-264 : 84-85

Hydraena compacta , new species

Figs. 73 (habitus), 75 (aedeagus), 262 (map)

Type Material. Holotype (male): Antananarivo, Ankaratra, Reserve Manjakatompo, lower riparian spring near affluent of station piscicole upstr. road to Lac Froid, 19° 21' S, 47° 18' E, 9 x 2001, Gerecke & Goldschmidt (MD 113a) (1 NMW). Paratypes (8): Same data as holotype (1 NMW); Antananarivo, Ankaratra (Antananarivo), Reserve Manjakatompo, left branch of the affluent to station piscicole, elev. 1770 m, 19° 21' S, 47° 18' E, 9 x 2001, Gerecke & Goldschmidt (MD 110) (4 NMW); Ankaratra (Antananarivo), Reserve Manjakatompo, right branch of the affluent to, station piscicole, 19° 21' S, 47° 18' E, 9 x 2001, Gerecke & Goldschmidt (MD 111) (3 NMW).

Differential Diagnosis. By virtue of its wide but compact body form and raised elytral intervals this species is one of the most distinctive Hydraena in Madagascar. The unusual aedeagus ( Fig. 75), which has a multispinose apical process, clearly indicates that this species is related to H. upsilonica ; but the habitus of the two species differ markedly ( Figs. 75, 76).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.84/0.90; head width 0.52; pronotum 0.47/0.69, PA 0.53, PB 0.59; elytra 1.14/0.90.

Dorsum black to piceous; legs dark brown; maxillary palpi dark brown, distal ½ of last palpomere not darker. Body form broad.

Head with clypeus finely moderately densely punctate; frons slightly more coarsely punctate laterally than medially where interstices ca. 1–3xpd, each puncture with short distinctive seta. Pronotum in anterior and posterior 1/3 more densely punctate than on disc, interstices narrow walls to ca. 0.5xpd; punctures on disc smaller, interstices ca. 1xpd, shining. Mentum finely punctate, shining; postmentum subscabrous. Genae raised, shining, with posterior ridge, interrupted in midline.

Pronotum arcuate laterally; anterior margin straight behind eyes, emarginate behind frons; PF1 and PF2 absent; PF3 and PF4 deep and confluent.

Elytra strongly arcuate laterally from midlength to apices; quite convex both longitudinally and transversely; summit of steep posterior declivity slightly before midlength; lateral explanate margins wide; serial punctures large, round, deep, separated by narrow walls, distinctly larger than largest pronotal punctures. Even numbered intervals 2–10 raised, subcostate. Apices in dorsal aspect rather sharply conjointly rounded, in posterior aspect margins not forming angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/0.5/2/1.3. P1 as wide as P2; median carina very weakly sinuate in profile. P2 l/w ca. 2/1, sides converging slightly posteriorly, apex rounded and on same level as anteromedian carina of metaventrite. Plaques carinate, converging anteriorly and joining anteromedian carina, together forming inverted Y-shape, separated basally by ca. 5x plaque width, located at sides of median depression. Metaventrite anteromedian carina slightly shorter than plaques; long longitudinal ridge on each side, extended posteriorly from margin of each mesocoxal cavity. AIS width at arcuate posterior margin ca. 1.5x P2. Protibia very slightly arcuate, slender. Mesotibia straight or very slightly arcuate, medial margin with 2 or 3 short sharp spines, spines longer and stronger from most proximal to most distal, surface of tibia notched immediately behind most distal spine. Metatibia straight, slender. Metafemur slender, arcuate on lateral margin, very weakly sinuate on medial margin. Abdominal apex with narrow apicomedian notch.

Etymology. Named in reference to the very compact and strong body form.