Megarthrus chiapas Rodríguez & Navarrete-Heredia & Arriaga-Varela & Cuccodoro 2020
Creators: name: Rodríguez, William David
name: Navarrete-Heredia, José L.
name: Arriaga-Varela, Emmanuel
name: Cuccodoro, Giulio
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Staphylinidae
Megarthrus
Megarthrus chiapas

description: Megarthrus chiapas Cuccodoro sp nov.
(Figs 1-26, 39)
http://zoobank.org:act: 1F284006-11C5-404A-8E68-E5C7668672EA
Type material. (7♂, 5♀). Holotype ♂: labeled MEXICO: Chiapas, 8 mi [= 12.9 km] N Pueblo Nuevo Solistahuacán, 6000’ [= 1830 m], 26-27.VIII.1973, A. Newton, berlese cloud forest litter, in FMNH. Paratypes (11): labaled with the same data as holotype, 2♂ and 1♀ in FMNH, 1 ♂ & 1♀ in MHNG and 1♂ in CZUG; labeled MEXICO: Chiapas, 8.9 km E Rayón, 1500m, 19.IX.1991, R. Anderson, 91-109, ex cloud forest litter, 1♂ and 2♀ in SEMC, 1 ♂ and 1♀ in MHNG.
Description. Habitus as in Figs 1–3. Combined length of head, pronotum and elytra = 1.3 - 1.4 mm; maximal pronotal width = 0.9 - 1.0 mm. Body chestnut brown, with lateral margins of pronotum and appendages slightly paler; 1, 2 or 3 yellowish apical antennomeres. Dorsal pubescence denser on head and pronotum than on elytral disc; medial frontal setae directed forward; elytral and pronotal setae almost straight, recumbent, becoming slightly denser along medial groove of pronotum and on anterior portion of elytral disc; pubescence on abdomen uniform, parallel, without macrosetae on sternites IV–VII. Frons, pronotum, humeral area of elytral and anterior portion of prohypomera granulate; frontal granulation conspicuous, with granules about as high as their diameter, or higher; elytral disc and metaventrite coarsely granulo-fossulate.
Frons above clypeus forming sharp ridge, the latter finely carinate, evenly; mesal portion of disc moderately convex in lateral view, evenly; anterior margin in dorsal view weakly arcuate in middle and laterally oblique; Ushaped frontal impression shallow. Temples convex, granulate. Occipital ridge indistinct. Antennae (Fig. 9) 1.8-2.0 times longer than pronotum.
Pronotum (Figs 25-26) with center strongly convex in frontal view; disc deeply depressed near middle of lateral edges, shallowly depressed along anterior and posterior margins; medial groove deep, parallel-sided, slightly arcu- ate in lateral view; hypomera granulate, with ridge extended from anterior margin to laterobasal angle (Fig. 26). Proventrite (Fig. 26) lacking medial ridge. Scutellum with anterior margin rounded; posterior margin laterally mod- erately arcuate toward strongly arcuate apex. Elytra gradually widened posteriorly (Fig. 1); disc with humeral callus strongly convex, two moderate swellings along anterior and posterior portions of suture, and moderately depressed posteriorly along lateral edge; the latter finely carinate, not denticulate, slightly arcuate in dorsal view.
Male: Frontoclypeal area not modified. Protarsomere 1 lacking ventral patch of modified adhesive setae. Mesofemora (Fig. 5) as long as metafemora. Mesotibiae (Fig. 6) shorter than metatibiae (Fig. 7), the latter straight. Metatarsomeres 1 about 1.3 times as long as combined length of metatarsomeres 2-4. Peg-like setae present only on mesotrochanters (Fig. 5; arranged in a row), on distal two thirds of mesotibiae (Fig. 6; arranged in 1-2 rows) and on distal half of metatibiae (Fig. 7; grouped in a field). Apex of abdomen as in Figs 10-11; tergite VIII as in Figs. 16-17, with apex mucronate in dorsal view; sternite VIII as in Fig. 14; segments IX-X as in Figs 12-13, with hemitergites IX as in Fig. 18 and sternite IX as in Fig 15. Aedeagus as in Figs 4 and 8, with dorsal valve triangular.
Female: Abdominal tergite VIII (Figs 23-24) forming a medioapical projection, with dorsal outline evenly convex in lateral view. Sternite VIII as in Fig. 22. Genital segments as in Figs 19-21; gonocoxal plate without me- diodorsal ridge.
Comparisons and diagnostic notes. Megarthrus chiapas Cuccodoro sp. nov. is easily distinguished from the Mexican M. altivagans and M. alatorreorum by the presence of a prohypomeral ridge (Fig. 26) and the medial frontal setae directed forward. It shares these features with M. flavosignatus Bierig (1940), M. zunilensis Sharp (1887), and M. cavianae Rodríguez, Navarrete-Heredia & Arriaga-Varela sp. nov., which are also the only other members of the genus to have the posterior margin of the male abdominal sternite VIII forming two projecting pointed processes (Figs 10, 11 and 14). Within these four species, the males of M. flavosignatus can be easily distinguished by the peglike setae on the mesotibiae arranged in a row (Cuccodoro 2011: Fig. 60) instead of grouped in a field (Figs 6 and 34; Cuccodoro 2011: Fig. 174), and by the metatibiae bearing peg-like setae only in distal third (Cuccodoro 2011: Fig. 59) intead of distal half (Figs 7 and 35; Cuccodoro 2011: Fig. 173). The males of three remaining species differ from each other by the shape of the tip of the abdominal tergite VIII, which is broadly rounded to slightly concave in M. zunilensis (Cuccodoro 2011: Fig. 176), mucronate in M. chiapas (Fig. 17), and sinuate in M. cavianae (Fig. 38). The shape of the aedeagus, notably that of the apical portion of the ventral wall, is diagnostic for the four species.
The female of M. flavosignatus is still unknown. However the mediodorsal margin of the valvifers is contiguous in apical half in M. zunilensis (Cuccodoro 2011: Fig. 180), while they are not contiguous in M. cavianae and M. chiapas (Fig. 19), and the posterior apical margin of the abdominal stenite VIII is evenly narrowed to subangulate apex in M. chiapas (Fig. 22), while it is slightly sinuate to rounded at apex in M. zunilensis (Cuccodoro 2011: Fig. 180), and deeply sinuate to rounded apex in M. cavianae (Fig. 30).
Distribution and natural history. Megarthrus chiapas Cuccodoro sp nov. in known only from the northwestern part of the Sierra Madre de Chiapas (Fig. 39), where specimens were collected at elevations ranging from 1500 to 1800 m sieving cloud forest’s leaf litter.
Etymology. The specific name is a noun in apposition derived from the type locality.
description: Published as part of Rodríguez, William David, Navarrete-Heredia, José L., Arriaga-Varela, Emmanuel & Cuccodoro, Giulio, 2020, Two new species of Megarthrus (Coleoptera, Staphylinidae, Proteininae) from Mexican Cloud Forests, pp. 571-583 in Zootaxa 4778 (3) on pages 572-578, DOI: 10.11646/zootaxa.4778.3.8, http://zenodo.org/record/3828825