Hydraena nanula, Perkins, 2017

Perkins, Philip D., 2017, Hydraenidae of Madagascar (Insecta: Coleoptera), Zootaxa 4342 (1), pp. 1-264 : 145-146

Hydraena nanula , new species

Figs. 131 (habitus), 133 (aedeagus), 291 (map)

Type Material. Holotype (male): Antsiranana, Ankarana, Ampositelo (three fossa creek) en route to Grand Tsingy , elev . 140 m, 12° 57' S, 49° 8' E, 1 xi–30 xii 2004, M. Balke (MD 018) ( ZSMC). Paratypes (31): Same data as holotype (7); Antsiranana, Ankarana, camp, waterhole at Andrafiabe cave entrance, elev . 50 m, 12° 57' S, 49° 8' E, 1 xi–30 xii 2004, M. Balke (MD 021) (10 ZSMC); Joffreville (M. d'Ambre , Antsiranana) Cascade sacre right riparian spring, hygropetric, elev . 1043 m, 12° 31' S, 49° 10' E, 23 iii 2011, R. Gerecke (MD 182) (1 NMW); Montagne des Francais , stream pool, elev . 171 m, 12° 20' S, 49° 20' E, 1 xi–30 xii 2004, M. Balke & D. Ottke (MD 001) (9 ZSMC); Fianarantsoa, Ranomafana, Talatakely, R. Fopognina , elev . 967 m, 21° 16' S, 47° 25' E, 1 xi–20 xii 2004, M. Balke & M. Monaghan (MD 027) (3 ZSMC); Toliara, Andohahela (Tulear), Isaka, W stream at the S National Park border (W RIP 118), pool, 24° 48' S, 46° 51' E, 9 ix 2001, Gerecke & Goldschmidt (MD 69b) (1 NMW).

Differential Diagnosis. Recognized by the combination of very small size (smallest in group; ca. 1.09 mm), the dark brown macula of the pronotum, and the very finely sparsely and shining dorsum. The aedeagus markedly differs from others in the study.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.09/0.48; head width 0.29; pronotum 0.26/0.37, PA 0.32, PB 0.34; elytra 0.66/0.48.

Dorsum of head with frons and clypeus dark brown to piceous, except clypeus lighter laterally; pronotum with dark brown macula, rather distinctly margined, borders widely light brown to testaceous, anterior border wider than posterior; elytra brown; legs light brown to testaceous; maxillary palpi testaceous, distal 0.5 of last palpomere not darker.

Frons and clypeus very finely very sparsely punctulate. Frons punctures much smaller than eye facets, interstices shining, 1–2xpd laterally, 2–6xpd medially., Clypeus effacedly microreticulate laterally. Mentum very sparsely very finely punctulate, strongly shining. Postmentum microreticulate, dull, no distinct median depression. Genae raised, shining, without posterior ridge.

Pronotum with lateral margins slightly sinuate, posterior angles nearly right angles; anterior margin straight behind eyes, emarginate in middle; disc very finely and very sparsely punctulate, punctures much smaller than eye facets, interstices strongly shining, ca. 5–8xpd; PF1 absent; PF2 very shallow; PF3 deep; PF4 absent.

Elytra weakly arcuate laterally; summit of posterior declivity near midlength; lateral explanate margins narrow; serial punctures very fine and sparse, ca. 1xpd of largest pronotal punctures. Intervals not raised, strongly shining, ca. 3–5xpd, as are interstices between punctures of a row. Apices in dorsal aspect conjointly rather sharply rounded, in posterior aspect margins forming very shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/0.8/2/1. P1 laminate; median carina sinuate in profile. P2 l/w ca. 3/1, sides slightly converging toward blunt apex, apex raised slightly above metaventral intercoxal process. Plaques moderately wide, converging and very narrowly separated anteriorly, very weakly raised, plaques separated posteriorly by ca. plaque width, located at sides of median depression. Metaventrite with very short longitudinal ridge on each side, extended posteriorly from margin of each mesocoxal cavity. AIS width at slightly arcuate posterior margin ca. 1.5x P2. Protibia very slightly arcuate, other tibiae straight, slender. Abdominal apex very weakly produced in small point.

Etymology. Named in reference to the small size.