Megarthrus inaequalis 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 : 113-114

Megarthrus inaequalis Bierig, 1940 Figs 8, 69-86

Megarthrus inaequalis Bierig, 1940: 379 . TYPE MATERIAL: Lectotype (Ƌ, in FMNH): “ Vara Blanca , viii.38, Costa Rica [hand-

written] / Typus”. – Paralectotypes (2): same data as lectotype, but “ Paratypus ”, 1 Ƌ in MHNG and 1 ♀ in FMNH, by present designation .

ADDITIONAL MATERIAL: COSTA RICA, Puntarenas, Monteverde Biol. Res. , trail near lab, 1550m, 21-22.v.1993 (Michalski) ex flight intercept trap, 1 Ƌ and 1 ♀ in SEMC ; same data, but 25.v.1993, 2 ♀♀ in MHNG and SEMC ; same data, but 26-28.v.1993, 2 ♀♀ in MHNG and SEMC ; same data, but 30.v.1993, 1 ♀ in SEMC ; same data, but near Quebrada cuecha, on Sendero Rio , 1580m, 13.v.1989 (Ashe, Leschen & Brooks) #163, ex Xylaria , 1 ♀ in SEMC ; same data, but 1500m, 1-4.vi.1979 (Campbell) 1 Ƌ in CNCI .

DESCRIPTION. Habitus as in Fig. 8. Combined length of pronotum and elytra = 1.3-1.5 mm; maximal pronotal width = 0.9-1.0 mm. Body dark brown with appendages 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 slightly arcuate, semi-erect; metasternal pubescence becoming denser posteriomedially, as long as or longer than that of prosternum; pubescence on abdominal tergites parallel, uniform; that on sternites 4-7 uniform. Frons, pronotum, elytra and anterior portion of prohypomera granulate; frontal granulation conspicuous, with granula about as high as their diameter, or higher; metasternum with granulofossulation becoming finer posteriomedially.

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 slightly evenly convex in lateral view; U-shaped frontal impression in middle deep, shallow laterally. Temples strongly convex in dorsal view. Antennae (Fig. 78) 2.1-2.3 times longer than pronotum.

Pronotum (Fig. 85) with center strongly convex in frontal view; disc deeply depressed near middle of lateral edges, shallowly depressed along anterior and posterior margins; medial groove slightly arcuate in lateral view, deep, parallel-sided; hypomera ridged from anterior margin to laterobasal angle, with a discal pit. Prosternal medial ridge present anteriorly, fine. Scutellum with anterior margin rounded and posterior margin slighly arcuate toward acutely angular apex.

Elytra gradually widened (Fig. 8); humeral callus raised, forming a blunt longitudinal ridge; disc with low anterior adsutural hump and conspicuous posterior adsutural hump, shallowly depressed posteriorly along lateral edges; the latter very finely carinate, moderately denticulate, slightly arcuate in dorsal view.

Abdominal sternites II and III with medial processes as in Fig. 86, posterior portion of process of sternite III widened.

Male: Frontoclypeal area not modified. Protarsomeres 1 lacking tenent setae. Mesofemora (Fig. 77) as long as metafemora. Mesotibiae (Fig. 72) shorter than metatibiae (Fig. 71). Metatarsomeres 1 about as long as combined length of metatarsomeres 2-4. Peg-like setae arranged in a single row on metatibia, grouped in a field on mesotrochanters (Fig. 77) and mesotibiae, and absent from protrochanters, profemora, protibiae, mesofemora, metatrochanters and metafemora. Apex of abdominal tergite VIII as in Figs 73, 75, 76. Sternite VIII as in Fig. 74. Sternite IX lacking subbasal protuberance. Aedeagus as in Figs 69, 70.

Female: Abdominal tergite VIII (Figs 83-84) lacking medioapical projection. Sternite VIII as in Fig. 82. Genital segments as in Figs 79-81; gonocoxal plate bearing a mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is apparently restricted to Costa Rica, at elevations ranging between 1500-1800 m. According to the original description, A. Bierig collected the types in shrubs bordering a primary forest at an elevation of 1800 m between Volcanoes Barba and Poás. Additional specimens were collected in Xylaria (fungi) or using flight intercept traps .

COMMENTS: Megarthrus inaequalis and M. mammiger are the only Neotropical members of the genus bearing conspicuous posterior adsutural humps. These two species can be easily distiguished by the shape of the pronotum, which is broadly notched laterobasally only in M. inaequalis . The diagnostic shape of the male abdominal tergite VIII of M. inaequalis is also particularly notable. See comments under M. adelphus and M. bierigi .