Hydraena casacolumna, Perkins, 2017

Perkins, Philip D., 2017, Hydraenidae of Madagascar (Insecta: Coleoptera), Zootaxa 4342 (1), pp. 1-264 : 53-54

Hydraena casacolumna , new species

Figs. 42 (habitus), 44 (aedeagus), 247 (map)

Type Material. Holotype (male): Fianarantsoa, Andringitra NP: Riambavy R. (female) cascade hygropetric habitat, N -22° 8.761, E:46° 53.4, wet rock surfaces next to high waterfall, elev. 1739 m, 8 v 2006, Bergsten et al. (P39) ( NHRS) . Paratypes (44): Same data as holotype (12); Fianarantsoa, Andringitra NP, ( Fianarantsoa ) , Cascade du Roi, elev. 1700 m, 22° 8' S, 46° 53' E, 14 iv 2011, R. Gerecke (MD 207) (1 NMW) ; Andringitra NP, (Fianarantsoa) , helocrenes crossing road right hand of Cascade du Roi, elev. 1710 m, 22° 8' S, 46° 53' E, 14 iv 2011, R. Gerecke (MD 208) (25 NMW) ; Andringitra NP, Riambavy R. (female) cascade fast flow over smooth horizontal surface, N:-22.14583, E:46.89154, elev. 1656 m, 22° 9' S, 46° 53' E, 8 v 2006, Monaghan et al. (P39BI03) (5 NHRS) ; Andringitra NP: Zomandao R., nr caves close to Camp Belamba , hygropetric and waterpools by the river, N -22° 8.192, E:46° 53.359, elev. 1601 m, 22° 8' S, 46° 53' E, 9 v 2006, Bergsten et al. (P39D) (1 NHRS) .

Differential Diagnosis. Differentiated from other members of the group by the shape of the metaventral plaques, which are elongate and more widely separated posteriorly than anteriorly. The aedeagus is quite narrow and long, and is easily distinguished from that of other members of the group. The sixth abdominal ventrite of females is densely setose in the posterior 1/2, and the long setae of the fifth ventrite are absent in the middle 1/4.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.53/0.69; head width 0.39; pronotum 0.38/0.49, PA 0.42, PB 0.43; elytra 0.97/0.69.

Dorsum dark brown, head darkest, nearly piceous; legs light brown; maxillary palpi light brown, distal ½ of last palpomere darker.

Head with clypeus moderately densely punctate and microreticulate, dull; frons punctures much larger and denser, interstices narrow walls to 0.5xpd, weakly shining, each puncture with short but distinctive seta. Pronotum densely moderately coarsely punctate; punctures in anterior and posterior 1/3 larger than those of head, interstices narrow walls to 0.5xpd; disc punctures slightly sparser, interstices ca. 0.5–1xpd, shining; each puncture with short but distinctive seta. Mentum sparsely finely punctulate, microreticulate, dull; postmentum microreticulate in shallow median depression, dull, lateral areas shining. Genae raised, shining, with well demarcated posterior ridge, interrupted in middle.

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

Elytra weakly arcuate laterally; summit of posterior declivity near midlength; lateral explanate margins moderately wide; serial punctures slightly rectangular, each with minute granule at anterior margin, ca. 0.5–1xpd. Intervals not raised, surface unequally, very weakly shining, ca. 0.5–1xpd. Apices in dorsal aspect conjointly rounded, in posterior aspect margins forming very shallow angle with one another.

Ratios of P2 width and plaque shape (P2/w/l/s) ca. 1/1/3/1. P1 almost as wide as P2; median carina weakly sinuate in profile. P2 l/w ca. 2.5/1, sides parallel, apex blunt and at same level as anteromedian carina of metaventrite. Plaques very large, elongate oval but tapering anteriorly, parallel or slightly arcuate, curve toward midline, narrowly separated, lateral margins at level of surrounding cuticle, medial margins slightly raised above surrounding cuticle, located at sides of narrow median depression. Metaventrite anteromedian carina slightly shorter than plaques, terminating between anterior extremes of plaques; long longitudinal ridge on each side, extended posteriorly from margin of each mesocoxal cavity to ca. midlength of metaventrite. AIS width at slightly arcuate posterior margin ca. 1.5x P2. All tibiae straight, moderately stout. Mesotibia medial margin slightly past midlength with 4–5 short stout spines, margin notched between spines. Metafemur lateral margin arcuate, medial margin weakly bisinuate. Abdominal apex with very small apicomedian notch.

Etymology. Named in reference to the "leaning" shape of the metaventral plaques.

Figures

FIGURE 42. Hydraena casacolumna, holotype, habitus dorsal, lateral, and ventral.