Megarthrus mastiger Bierig, 1940

Cuccodoro, Giulio, 2011, Revision of the Neotropical types of Megarthrus Curtis, 1829 and description of two new species from Costa Rica and Peru (Coleoptera, Staphylinidae, Proteininae), Revue suisse de Zoologie 118 (1), pp. 107-147 : 117-118

Megarthrus mastiger Bierig, 1940 Figs 9, 124-142

Megarthrus mastiger Bierig, 1940: 376 .

TYPE MATERIAL: Lectotype (Ƌ, in FMNH): “ Vara Blanca , viii.38, Costa Rica [handwritten]” . Paralectotypes (4): Same data as lectotype, 2 ƋƋ and 2 ♀♀ in FMNH and MHNG, by present designation .

ADDITIONAL MATERIAL: COSTA RICA, Puntarenas, Monte Verde , 1520m, 14.v.1989 (Ashe, Brooks & Leschen) flight intercept traps, #177, 1 ♀ in SEMC .

DESCRIPTION: Habitus as in Fig. 9. Combined length of pronotum and elytra = 1.5-1.7 mm; maximal pronotal width = 1.0- 1.1 mm. Body dark brown with appendages slightly paler; antennomeres 10-11 paler than antennomeres 1-9. Dorsal pubescence uniform; frontal setae directed forward; elytral and pronotal setae fairly straight, recumbent; metasternal pubescence uniform, shorter than prosternal; pubescence on abdominal tergites parallel, uniform; that on sternites IV-VII uniform, except for a pair of subapical macrosetae setae on each sternite. Frons, pronotum, elytra and anterior portion of prohypomera granulate; frontal granulation inconspicuous, with granula about as high as half of their diameter, or higher; pronotum granulofossulate; metasternum with granulofossulation becoming finer posteriomedially.

Frons forming above clypeus a sharp ridge, the latter finely evenly carinate, evenly arcuate in dorsal view; mesal portion of disc strongly evenly convex in lateral view; U-shaped frontal impression deep in middle, shallow laterally. Temples strongly convex in dorsal view. Antennae (Fig. 137) 2.2-2.4 times longer than pronotum.

Pronotum (Fig. 141) with center moderately convex in frontal view; disc deeply depressed near middle of lateral edges, shallowly depressed along anterior margin, posterior margin and posterior portion of medial groove; the latter nearly straight in lateral view, deep, parallel-sided; hypomera ridged from anterior margin to laterobasal angle, with a discal pit. Prosternal medial ridge absent. Scutellum with anterior margin subangulate in middle and posterior margin strongly arcuate toward obtusely angled apex.

Elytra gradually widened (Fig. 9); humeral callus low, moderately convex; disc with low adscutellar hump, shallowly depressed posteriorly along lateral edge; the latter finely carinate, finely denticulate, somewhat sinuate in dorsal view.

Abdominal sternites II and III with medial processes as in Fig. 142, posterior portion of process of sternite III straight.

Male: Frontoclypeal area not modified. Protarsomeres 1 lacking tenent setae. Mesofemora (Fig. 128) shorter than metafemora (Fig. 130). Mesotibiae (Fig. 127) shorter than metatibiae (Fig. 126). Metatarsomeres 1 somewhat shorter than combined length of metatarsomeres 2-4. Peg-like setae arranged in a single row on mesotrochanters (Fig. 128), grouped in a field on mesotibiae and metatibiae, and absent from protrochanters, profemora, protibiae, mesofemora, metatrochanters (Figs 130, 133) and metafemora. Apex of abdominal tergite VIII as in Figs 129, 131. Sternite VIII as in Fig. 132. Sternite IX lacking subbasal protuberance. Aedeagus as in Figs 124-125.

Female: Abdominal tergite VIII (Figs 139-140) lacking a medioapical projection. Sternite VIII as in Fig. 138. Genital segments as in Figs 134-136; gonocoxal plate lacking a mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is known only from Costa Rica, where it was found at elevations ranging between 1500 and 1800 m. According to the original description, A. Bierig collected the types between the Volcanoes Barba and Poás, at 1800 m in cow dung and decaying leaves of shrubs at forest margins.

COMMENTS: The species differs from all the other Neotropical Megarthrus by the particularly narrow mediobasal projection af the abdominal sternite VIII. The presence of a small projecting process on the metatrochanter in the male is only shared with M. mammiger , which differs notably from M. mastiger by the lateral contour of the pronotum, and by the presence on the female of a mediodorsal ridge on the gonocoxal plate. See comments under M. adelphus .