Balligratus gracilis, Moret, Pierre & Ortuño, Vicente M., 2017

Moret, Pierre & Ortuño, Vicente M., 2017, Balligratus, new genus of wingless ground beetles from equatorial Andean montane forest (Coleoptera: Carabidae: Lachnophorini), Zootaxa 4258 (2), pp. 101-120 : 108-111

Balligratus gracilis sp. nov.

Holotype, ♂, ECUADOR: Provincia Sucumbios, km 6 East Santa Bárbara , 2,600 m, 28.VII.1998, leg. P. Moret & I. Tapia ( MNHN). Only known specimen.

Description. Overall body length: 5.70 mm. Slender species with narrow elytra and rounded humeri ( Fig. 5 ). Body tegument brunneopiceous, shiny; appendages and labrum testaceous; clypeus flavocastaneous.

Dimensions of the head: HL 0.75 mm, HW 1.04 mm. Disc with a weak isodiametric microsculpture. Antennae reaching the basal third of the elytra when laid along side margin. Labium: Fig. 6 g.

Pronotum large (PL 1.14 mm; PW 1.42 mm), feebly transverse (PL/PW = 0.80), wider than head, convex, trapezoidal in shape, its maximum width at middle. Microsculpture of the disc transverse and shallow. Sides arcuate anterad, subrectilinear in basal half and convergent backwards; hind angles obtuse-rounded. Anterior angles feebly produced; lateral groove narrow; basal margin weakly sinuate medially; basolateral depressions obsolete. Lateral seta inserted at base of the distal third of the lateral margin. Prosternal apophysis elongate, subelliptical at apex, distinctly bordered along basal margins ( Fig. 6 h).

Elytra relatively large (EL: 3.19 mm; EW: 1.91 mm; EW/EL = 0.59; PW/EW = 0.74), suboval in shape, almost subparallel medially, with narrowed and weakly developed humeri. Maximum width at middle. Basal bead sinuate. Elytral suture dehiscent at apex. Microsculpture of the disc transverse and shallow. All striae deep and well impressed, especially the basal third of striae 5 to 7; intervals almost flat. Scutellar striole well marked. Anterior discal seta adjoining the 3rd stria at the height of the 4th or 5th seta of the umbilicate series; postmedian seta adjoining the 2nd stria at the middle of elytron; 13 umbilicate setae in the ninth interval, distributed 5 / 1 / 7.

Legs moderately slender; meso- and metatarsi elongate in relation to the overall body length (MstL 0.93 mm; MttL 1.39 mm; [MstL+MttL]/BL = 0.40). Basal three tarsomeres slightly bisulcate dorsally, sulci deeper on the first tarsomere.

Apical margin of the last visible abdominal ventrite arcuate laterally, almost truncate medially ( Fig. 6 a).

Male genitalia ( Fig. 6 b–f): median lobe relatively small (MLL 1.20 mm; MLL/BL= 0.21), arcuate in lateral view, pyriform in dorsal view; ventral margin entirely sinuate; apex elongate, gradually narrowed, with an obtusely hooked ending; basal bulb reduced. Left paramere large, oval-shaped; right paramere small, bifid apically, with a hook-like basal process. Ring sclerite elongate, narrowly ovate.

Female unknown.

Comment. The only known specimen shows a short anastomosis of striae 3 and 4 near the base of the right elytron.

Etymology. Latin adjective meaning “slender”.

Distribution. Pacific slope of the Western Cordillera in Northern Ecuador, close to the border with Colombia, in the upper montane forest ( Fig. 11 ). Type locality at 0°38’23” N / 77°29’27” W.

Way of life. The holotype was found at the beginning of the night (7:30–8:30 PM), foraging on the surface of the leaf litter.

Figures

FIGURE 5. Balligratus gracilis sp. nov., male holotype, habitus in dorsal view. Scale bar: 1 mm.

FIGURE 6. Balligratus gracilis sp. nov., details of ventral side and male genitalia. a: last visible abdominal ventrite (male); b: ring sclerite; c: median lobe, left lateral view; d: left paramere; e: right paramere; f: median lobe, dorsal view; g: labium; h: prosternal apophysis. Scale bars: 0.5 mm.

FIGURE 11. Distribution of Balligratus gen. nov. in Ecuador. The ochre to brown area roughly corresponds to the montane pluvial forest. White squares: described species; black squares: undescribed species. Map base © OpenStreetMap contributors.