Megarthrus altivagans Bernhauer, 1929

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 : 109-111

Megarthrus altivagans Bernhauer, 1929 Figs 1, 21-38

Megarthrus altivagans Bernhauer, 1929: 187 .

TYPE MATERIAL: Holotype (♀, in FMNH): “Mex. Desierto de los Leones, 20.vii.24, Dampf [handwritten] [handwritten underneath the card: esiero Leones 23. Dampf] / wald. 3- 4000m, in rotgelbem Blätterpilz. [handwritten] / un. F. 247 Desierto 20/vii.24, rotgelbem Blätterpilz [handwritten] / Megarthrus altivagans Brnh. Typus unic [handwritten]”.

ADDITIONAL MATERIAL: MEXICO, Jalisco, E slope of Nevado de Colima, 19mi W Alenquique <103°36'W; 19°32'N> ca. 3000m, 20-21.ix.1973 (Newton) 547 Cs, #73-1125, ex squid carrion trap in Alnus woodland, 1 Ƌ in FMNH and 1 ♀ in MHNG ; same data, but ca. 2400m, 21.ix.1973, berlese, ex mixed hardwood pine forest, 1 ♀ in FMNH ; same data, but 21-22.ix.1973, on gilled mushrooms, 1 ♀ in FMNH . – Mexico, Volc. Popocatépetl, Km 10, ca. 3000m, 9.v.1971 (Campbell), 1 Ƌ in CNCI .

DESCRIPTION: Habitus as in Fig. 1. Combined length of pronotum and elytra = 1.4-1.7 mm; maximal pronotal width = 0.9-1.1 mm. Body dark brown with appendages slightly paler. Dorsal pubescence uniform; medial frontal directed backward; elytral and pronotal pubescence slightly arcuate, recumbent; metasternal pubescence becoming sparser posteriomedially and longer anteriorly, shorter than prosternal pubescence; pubescence on abdominal tergites parallel, uniform. Frons and anterior portion of prohypomera granulate; frontal granulation fine, with granula lower than half of their diameter. Pronotum, elytra and lateral portions of metasternum granulofossulate; posteriomedial portion of metasternum impunctate.

Frons forming above clypeus a sharp ridge, the latter not carinate; mesal portion of disc weakly evenly convex in lateral view; U-shaped frontal impression shallow. Temples nearly flat in dorsal view. Antennae (Fig. 30) 1.9-2.1 times longer than pronotum.

Pronotum (Fig. 37) with center moderately convex in frontal view; disc shallowly depressed along lateral edges; medial groove nearly straight in lateral view, shallow, parallel-sided; hypomera without discal ridge, nor pit. Prosternal medial ridge absent. Scutellum with anterior margin fairly right-angled in midlle and posterior margin slighly arcuate toward acutely angular apex.

Elytra gradually widened (Fig. 1); humeral callus oboslete; disc with very low swellings, nearly flat 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. 38, posterior portion of process of sternite III straight.

Male: Anterior frontal edge raised in middle, horn-like. Protarsomeres 1 bearing tenent setae. Metafemora about as long as mesofemora (Fig. 29). Metatibiae (Fig. 23) longer than mesotibiae (Fig. 24). Metatarsomeres 1 shorter than combined length of metatarsomeres 2-4. Peg-like setae arranged in a double row on mesotrochanters (Fig. 29) and mesotibiae, in a single row on metatibiae, and absent from protrochanters, profemora, protibiae, mesofemora, metatrochanters and metafemora. Pubescence on sternites IV-VII becoming denser posteriomedially. Apex of abdominal tergite VIII as in Figs 27-28. Sternite VIII as in Fig. 26. Hemitergites IX as in Fig. 25. Sternite IX lacking subbasal protuberance. Aedeagus as in Figs 21-22.

Female: Anterior frontal edge evenly arcuate in dorsal view. Abdominal tergite VIII (Figs 35-36) lacking medioapical projection. Pubescence on sternites IV-VII uniform, except for a pair of subapical macrosetae on each sternite. Sternite VIII as in Fig. 34. Genital segments as in Figs 31-33; gonocoxal plate lacking mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is from Mexico, where it occurs in the vicinity of Mexico city (Parque Nacional Desierto de Los Leones and Parque Nacional Ixtaccihualtl-Popocatépetl) and about 450 km west in the Parque Nacional Nevado de Colima. Megarthrus altivagans has been collected in mixed hardwood pine forests and Alnus woodlands at elevations ranging from 2400-4000 m by

sifting forest litter, in gilled mushrooms, and using squid carrion traps. Two large oval eggs (0.8 x 0.3 mm) were found in the abdomen of the holotype.

COMMENTS: Megarthrus altivagans is so far the only Neotropical Megarthrus having the frontal setae directed backward and bearing adhesive setae on the first protarsomeres in the male. Also, the medially raised, horn-like frontal margin in the male is distinctive. It strongly resembles M. ashei Cuccodoro & Löbl, 1996 , from the Rocky Mountains of Arizona and New Mexico, which has a slightly different aedeagus and the frons unmodified in the male.