Hydraena tripartita, Perkins, 2017

Perkins, Philip D., 2017, Hydraenidae of Madagascar (Insecta: Coleoptera), Zootaxa 4342 (1), pp. 1-264 : 88-89

Hydraena tripartita , new species

Figs. 77 (habitus), 79 (aedeagus), 264 (map)

Type Material. Holotype (male): Fianarantsoa, Ranomena , river NW from the 1.07 km-railway-tunnel, pool, elev. 950 m, 23° 25' S, 47° 16' E, 19 viii 2001, Gerecke & Goldschmidt (MD 34c) ( NMW) . Paratypes (10): Same data as holotype (1 NMW). Fianarantsoa, Matsiara Ambony, Ranomafana NP, next to Sahamalaotra trail entrance; forest stream with sandy bottom, elev. 1130 m, 21.2395S 47.3947E, 2 xi 2014, P. D. Perkins ( MAD14- 04 ) (9 MCZ).

Differential Diagnosis. Differentiated from other members of the group by the comparatively short elytra that have apices conjointly sharply rounded. The aedeagus, which has three distal processes, cannot be confused with others.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.72/0.73; head width 0.41; pronotum 0.39/0.55, PA 0.44, PB 0.45; elytra 0.94/0.73.

Dorsum dark brown to piceous; legs dark brown; maxillary palpi light brown.

Head with clypeus moderately finely and moderately sparsely punctate, lateral margins microreticulate; frons coarsely densely punctate near eyes, interstices narrow walls, weakly shining, disc less coarsely and less densely punctate, interstices 1–2xpd, shining. Pronotum moderately coarsely and moderately densely punctate, punctures in anterior and posterior larger than those on disc; interstices 1–2xpd, shining. Mentum moderately densely, moderately coarsely punctate, interstices shining; postmentum densely coarsely punctate, subrugose. Genae raised, non-punctate reliefs shining, posterior ridge well delimited by coarsely punctate sulcus.

Pronotum sinuate laterally, distinctly narrowed basally, almost subcordate; anterior margin straight behind eyes, emarginate behind frons; PF1 and PF2 very shallow or absent; PF3 and PF4 deep, confluent.

Elytra arcuate laterally; posterior declivity steep, summit near midlength, elytra appearing slightly humped; elytra transversely very convex, especially at posterior 3/5; lateral explanate margins wide; serial punctures round, distinctly larger than punctures on pronotal disc, interstices 0.5–1xpd, shining. Apices in dorsal aspect conjointly sharply rounded, almost acuminate, in posterior aspect margins do not form angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s [posteriorly]) ca. 1/0.2/1.5/1. P1 slightly narrower than P2; median carina very weakly sinuate in profile. P2 l/w ca. 2/1, sides converging posteriorly, apex blunt and on same level as anteromedian carina of metaventrite. Plaques very narrow, strongly carinate lines, converging anteriorly and joining anteromedian carina, together forming inverted Y-shape, separated basally by ca. 4x plaque width, located at sides of deep median depression; area lateral to plaques concave. Metaventrite anteromedian carina strong, ca. same length as plaques; long longitudinal and slightly arcuate ridge on each side, extended posteriorly from margin of each mesocoxal cavity. AIS width at arcuate posterior margin ca. 1.5x P2. All tibiae straight, slender. Mesotibia medial margin near midlength with 2–3 very short sharp spines, margin shallowly notched between spines. Metafemur slender, arcuate on lateral margin, very weakly sinuate on medial margin. Abdominal apex with small apicomedian notch.

Etymology. Named in reference to the three processes of the aedeagus, and the three parts of the metaventral inverted Y-shaped carinae.

Remarks. The holotype is solid black, but teneral specimens collected under decaying leaves on a cascade at Ranomafana N.P. have a distinct pronotal fascia, and lighter elytra.