Megarthrus adelphus Bierig, 2011

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 : 108-109

Megarthrus adelphus Bierig stat. nov. Figs 10, 12-20

Megarthrus solitarius adelphus Bierig, 1940: 377 .

TYPE MATERIAL: Lectotype (♀, in FMNH): “ Carpintera , 6.viii.39. Costa Rica [handwritten] / Typus ” . – Paralectotypes (2 ♀♀): same data as lectotype, but “ Paratypus ”, in FMNH, and MHNG by present designation .

DESCRIPTION: Habitus as in Fig. 10. Combined length of pronotum and elytra = 1.3-1.4 mm; maximal pronotal width = 0.9-1.1 mm. Body dark brown with appendages slightly paler; antennomeres 11 paler than antennomeres 1-10. Dorsal pubescence fairly uniform, denser on head and pronotum than on elytral disc; frontal setae directed forward; elytral and pronotal setae slightly arcuate, recumbent; metasternal pubescence fairly uniform, as long as or longer than that of prosternum; pubescence on abdominal tergites parallel, uniform; that on sternites IV-VII 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 denser and finer posteriomedially.

Frons forming above clypeus a sharp ridge, the latter finely 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. 12) 2.3-2.5 times as long as pronotum.

Pronotum (Fig. 19) with center strongly 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 slightly arcuate 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 rounded, posterior margin slightly arcuate toward acutely angular apex.

Elytra gradually widened (Fig. 10); humeral callus low, moderately convex; disc with low swellings, moderately depressed posteriorly along lateral edge; the latter finely carinate, indistinctly denticulate, slightly arcuate in dorsal view.

Abdominal sternites II and III with medial processes as in Fig. 20, posterior portion of process of sternite III trifid.

Male: Unknown.

Female: Abdominal tergite VIII (Figs 16, 17) lacking medioapical projection. Sternite VIII as in Fig. 18. Genital segments as in Figs 13-15; gonocoxal plate bearing a mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is known only from Costa Rica. According to the original description, the types were collected by A. Bierig at 1800 m from sifted leaf litter near a fallen tree in a forest (together with the holotype of M. flavosignatus ).

COMMENTS: Megarthrus adelphus , M. bierigi , M. inaequalis , M. machu and M. mastiger share a laterobasally broadly notched pronotum. Among these species, M. adelphus is easily distinguished the lateral contour of its pronotum forming four denticles.