Megarthrus chiapas Cuccodoro

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, Zootaxa 4778 (3), pp. 571-583: 572-578

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Megarthrus chiapas Cuccodoro


Megarthrus chiapas Cuccodoro  sp nov.

( Figs 1-26View FIGURES 1–3View FIGURES 4–9View FIGURES 10–18View FIGURES 19–24View FIGURES 25–28, 39View FIGURE 39) 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 1–3View FIGURES 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. 9View FIGURES 4–9) 1.8-2.0 times longer than pronotum.

Pronotum ( Figs 25-26View FIGURES 25–28) 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. 26View FIGURES 25–28). Proventrite ( Fig. 26View FIGURES 25–28) lacking medial ridge. Scutellum with anterior margin rounded; posterior margin laterally mod- erately arcuate toward strongly arcuate apex. Elytra gradually widened posteriorly ( Fig. 1View FIGURES 1–3); 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. 5View FIGURES 4–9) as long as metafemora. Mesotibiae ( Fig. 6View FIGURES 4–9) shorter than metatibiae ( Fig. 7View FIGURES 4–9), 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. 5View FIGURES 4–9; arranged in a row), on distal two thirds of mesotibiae ( Fig. 6View FIGURES 4–9; arranged in 1-2 rows) and on distal half of metatibiae ( Fig. 7View FIGURES 4–9; grouped in a field). Apex of abdomen as in Figs 10-11View FIGURES 10–18; tergite VIII as in Figs. 16-17View FIGURES 10–18, with apex mucronate in dorsal view; sternite VIII as in Fig. 14View FIGURES 10–18; segments IX-X as in Figs 12-13View FIGURES 10–18, with hemitergites IX as in Fig. 18View FIGURES 10–18 and sternite IX as in Fig 15View FIGURES 10–18. Aedeagus as in Figs 4 and 8View FIGURES 4–9, with dorsal valve triangular.

Female: Abdominal tergite VIII ( Figs 23-24View FIGURES 19–24) forming a medioapical projection, with dorsal outline evenly convex in lateral view. Sternite VIII as in Fig. 22View FIGURES 19–24. Genital segments as in Figs 19-21View FIGURES 19–24; 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. 26View FIGURES 25–28) 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 14View FIGURES 10–18). 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 6View FIGURES 4–9 and 34View FIGURES 32–38; 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 7View FIGURES 4–9 and 35View FIGURES 32–38; 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. 17View FIGURES 10–18), and sinuate in M. cavianae  ( Fig. 38View FIGURES 32–38). 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. 19View FIGURES 19–24), and the posterior apical margin of the abdominal stenite VIII is evenly narrowed to subangulate apex in M. chiapas  ( Fig. 22View FIGURES 19–24), 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. 30View FIGURES 29–31).

Distribution and natural history. Megarthrus chiapas Cuccodoro  sp nov. in known only from the northwestern part of the Sierra Madre de Chiapas ( Fig. 39View FIGURE 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.


Field Museum of Natural History


Universidad de Guadalajara,Centro de Estudios en Zoologia, Entomologia


University of Kansas - Biodiversity Institute