Megarthrus zunilensis Sharp, 1887

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 : 120-122

Megarthrus zunilensis Sharp, 1887 Figs 6, 171-187

Megarthrus zunilensis Sharp, 1887: 743 .

TYPE MATERIAL: Lectotype (Ƌ, in BMNH): “ Megarthrus zunilensis . Type D. S., Cerro Zunil . Guatem., Champion [Sharp’s handwritting] | Cerro Zunil, Guatemala, Champion | B.C.A. Col. 1. 2. Megarthrus zunilensis Sharp ” . – Paralectotypes (2 ♀♀ in BMNH): same data as lectotype, but “Sp. figured”; same data as lectotype, but “ Cerro Zunil , 4-5000 ft., Champion”, by present designation .

ADDITIONAL MATERIAL: COSTA RICA, Puntarenas, Monteverde Biol. Res. , ca. 1500m, 23-24.v.1979 (Campbell) 1 Ƌ in CNCI . – GUATEMALA, Quetzaltenango, 14.2km SW Zunil , 1340m, 20.vi.1993 (Génier) ex human faeces trap, 1 ♀ in SEMC . – Sacatepequez, 4.5km SW san Miguel, Duenas , 1760m, 12.vi.1991 (Anderson) #91-61, ex mesic hardwood litter, 1 Ƌ in SEMC . – Zacapa, 3.5km SE La Union , 1500m, 4.vi.1991 (Anderson) #91-50, ex cloud forest litter, 1♀ in SEMC ; same data, but 23-25.vi.1993 (Brooks & Ashe) #103, ex flight intercept trap, 1 ♀ in MHNG . – HONDURAS, Santa Barbara, Mt. Santa Barbara, 11.5km S & 5.6km W Peñ a Blanca <14°57'N; 88°05'W> 1800m, 20.vi.1994 (Brooks & Ashe) #163, ex decaying slash, 2 ƋƋ and 2 ♀♀ in MHNG and SEMC ; same data, but #164, ex treefall litter, 1 Ƌ and 2 ♀♀ in SEMC . – NICARAGUA, El Cerro Cimborazo <13°02'N; 85°56'W> 1400m, 20.xi.1971 (Stockwell) 1 Ƌ in FMNH .

DESCRIPTION: Habitus as in Fig. 6. Combined length of pronotum and elytra = 1.4-1.5 mm; maximal pronotal width = 1.0- 1.1 mm. Body dark brown wih appendages slightly paler; antennomeres 10-11 paler than antennomeres 1-9. Dorsal pubescence denser on head and pronotum than on elytral disc, becoming denser along medial groove of pronotum and on anterior portion of elytral disc; frontal setae directed forward; elytral and pronotal setae slightly arcuate, recumbent; metasternal pubescence becoming denser anteriorly, longer than that of prosternum; pubescence on abdominal tergites parallel, uniform; that on sternites IV-VII uniform. Frons, pronotum, lateral portion of elytral disc and anterior portion of prohypomera granulate; frontal granulation conspicuous, with granula about as high as their diameter, or higher; metasternum coarsely granulofossulate.

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 shallow. Temples strongly convex in dorsal view. Antennae (Fig. 182) 2.1-2.3 times longer than pronotum.

Pronotum (Fig. 186) 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, disc without pit. Prosternal medial ridge absent. Scutellum with anterior margin rounded and posterior margin slighly arcuate toward acutely angular apex.

Elytra gradually widened (Fig. 6); 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. 184, posterior portion of process of sternite III straight.

Male: Frontoclypeal area not modified. Protarsomere 1 lacking tenent setae. Mesofemora (Fig. 175) as long as metafemora. Mesotibiae (Fig. 174) shorter than metatibiae (Fig. 173). Metatarsomeres 1 about as long as combined length of metatarsomeres 2-4. Peg-like setae arranged in a single row on mesotrochanters (Fig. 175), grouped in a field on mesotibiae and metatibiae, and absent from protrochanters, profemora, protibiae, mesofemora, metatrochanters and metafemora. Apex of abdominal tergite VIII as in Figs 176, 178. Sternite VIII as in Fig. 177. Sternite IX lacking subbasal protuberance. Aedeagus as in Figs 171-172.

Female: Abdominal tergite VIII (Figs 185, 187) bearing medioapical projection. Sternite VIII as in Fig. 183. Genital segments as in Figs 179-181; gonocoxal plate lacking a mediodorsal ridge.

DISTRIBUTION AND NATURAL HISTORY: The species is known from Costa Rica, Guatemala, Honduras and Nicaragua. It was collected by sifting leaf litter or using flight intercept and faeces traps in mesic hardwood forests and cloud forests at elevations ranging between 1300 and 3100m. It is the most widespread Megarthrus treated in this study.

COMMENTS: Among Neotropical Megarthrus , M. zunilensis is particularly notable by the gonocoxal plate lacking a mediodorsal ridge in females, in combination with the frontal setae directed forward and the eleventh antennomere ovoid. The latter two characters are shared only with M. flavosignatus , of which only the male is known and which has a differently shaped aedeagus. See comments under M. flavosignatus .