Megarthrus mammiger 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 : 116-117

Megarthrus mammiger Bierig, 1940 Figs 2, 105-123

Megarthrus mammiger Bierig, 1940: 375 . TYPE MATERIAL: Lectotype (Ƌ, in FMNH): “ Vara Blanca , viii.38, Costa Rica [hand-

written] / Typus”. – Paralectotype (1 ♀, in FMNH): same data as lectotype, but “ Paratypus ”, by present designation .

ADDITIONAL MATERIAL: COSTA RICA, Hwy #2, km 93 <83°45'W; 9°36'N> 3200m, iv.1985 (Goulet & Masner), 1 Ƌ in CNCI . – Puntarenas, Monte Verde, Cerro Amigos , 1780m, 21.v.1989 (Ashe, Brooks & Leschen) flight intercept trap, #315, 1 Ƌ and 1 ♀ in SEMC . – Volc. Irazú , 2800m, 18.i.1940 (Bierig), 1 Ƌ in MHNG . – El Jardiú, ca. 3000m, 19.v.1944 (Bierig), 1 Ƌ in FMNH . – San Isidro de il Tajar, ca. 1500m, 19.v.1944 (Bierig), 1 ♀ in MHNG .

DESCRIPTION: Habitus as in Fig. 2. Combined length of pronotum and elytra = 1.8-1.9 mm; maximal pronotal width = 1.3 mm. Body dark brown with appendages and elytra slightly paler; antennomeres 10-11 paler than antennomeres 1-9. Dorsal pubescence fairly uniform, denser on head and pronotum than on elytral disc; frontal setae directed forward; elytral and pronotal setae fairly straight, recumbent; metasternal pubescence fairly uniform, shorter than prosternal; pubescence on abdominal tergites parallel, uniform. Frons, anterior portion of prohypomera, humeral callus and lateral area of elytral disc granulate; frontal granulation inconspicuous, with granula about as high as half of their diameter; pronotum granulofossulate; metasternum with granulofossulation becoming finer posteriomedially; adsutural half of elytral disc punctate.

Frons forming above clypeus a sharp ridge, the latter finely evenly carinate, weakly arcuate in middle and laterally oblique 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. 115) 2.3-2.6 times longer than pronotum.

Pronotum (Fig. 123) with center strongly convex in frontal view; disc deeply depressed near middle of lateral edges, shallowly depressed along anterior and posterior margins; medial groove nearly straight in lateral view, deep, somewhat narrowed in middle; hypomera ridged from anterior margin to laterobasal angle, disc without pit. Prosternal medial ridge absent. Scutellum with anterior margin angulate in middle and posterior margin slighly arcuate toward right-angled apex.

Elytra gradually widened (Fig. 2); humeral callus raised, forming a blunt longitudinal ridge; disc with low anterior and posterior adsutural humps, moderately depressed posteriorly along lateral edge; the latter finely carinate, finely denticulate, nearly straight in dorsal view.

Abdominal sternites II and III with medial processes as in Fig. 120, posterior portion of process of sternite III trifid.

Male: Frontoclypeal area not modified. Protarsomeres 1 lacking tenent setae. Mesofemora (Fig. 111) as long as metafemora (Fig. 110). Mesotibiae (Fig. 107) shorter than metatibiae (Fig. 108). Metatarsomeres 1 about as long as combined length of metatarsomeres 2-4. Peg-like setae arranged in a single row on mesotrochanters (Fig. 111), mesotibiae and metatibiae, absent from protrochanters, profemora, protibiae, mesofemora, metatrochanters metatrochanter (Figs 109-110) and metafemora; metatrochanters with a projecting process. Pubescence on sternites IV-VII becoming denser posteriomedially. Apex of abdominal tergite VIII as in Figs 113, 114. Sternite VIII as in Fig. 112. Sternite IX lacking subbasal protuberance. Aedeagus as in Figs 105-106.

Female: Pubescence on sternites IV-VII uniform, except for a pair of subapical macrosetae on each sternite. Abdominal tergite VIII (Figs 121-122) without medioapical projection. Sternite VIII as in Fig. 119. Genital segments as in Figs 116-118; gonocoxal plate bearing a mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is known only from Costa Rica, where it was found at elevations ranging from 1500-3200 m. According to the original description, A. Bierig collected the types between the Volcanoes Barba and Poás, at 1800 m in cow dung and in dead bamboo leaves .

COMMENTS: Among the Neotropical Megarthrus possessing a conspicuous humeral callus (see comments under M. bierigi ), M. mammiger can be easily recognised by its laterobasally shallowly emarginated pronotum. See also comments under M. inaequalis and M. mastiger .