Megarthrus chujiao Liu and Cuccodoro, 2020

Liu, Zhiping & Cuccodoro, Giulio, 2020, Megarthrus of China. Part 1. Description of a new species resembling M. antennalis Cameron, 1941 (Coleoptera: Staphylinidae: Proteininae), Zootaxa 4750 (2), pp. 269-276 : 270-275

Megarthrus chujiao Liu and Cuccodoro , sp. nov.

( Figs. 3–29 )

Type material. Holotype, male “ China: N-Sichuan [CH12-26], 70km N Songpan, road S 301, above Gan lake , 33°15’26’’N, 103°46’03’’E, 2700m, spruce forest with birch, litter, mushroom, moss, and dead wood sifted, 12.VIII.2012, M. Schülke ” (cSch).

Paratypes: same data as holotype, 6 males, in cSch, MHNG and SWUC; “ China [26]—N-Sichuan, N Songpan, 33°15’26’’N, 103°46’03’’E, 2700m, spruce forest with birch, 12.viii.2012, V. Assing”, 2 males in cAss and MHNG; “ China, W-Sichuan (13) Daxue Shan, Hailuogou Glacier Park, Camp 1, 2100m, 29°36’00’’N, 102°03’35’’E, 27.– 31.05.1997, M. Schülke ”, 1 male and 1 female, in MHNG and cSch; “ China: Sichuan, Gongga Shan, above Camp 2 [29°57’ N, 102°00’ E], 2850m, 26.VII.1994, A. Smetana, [C25]”, 1 male, in MHNG; “ China: Yunnan: [CH07-28], Nujiang Lisu Aut. Pref., Gaoligong Shan, side valley 19km NW Liuku , 25°59’02’’N, 98°42’23’’E, 2730m, devast, prim, forest, litter sifted, 9.VI.2007, A. Pütz ”, 4 males, in MHNG and cPüt .

Description. Habitus as in Figs. 3–4 . Combined length of head, pronotum and elytra 1.8–2.1 mm; maximal pronotal width= 0.9–1.1 mm. Body and appendages predominantly rust brown, with head darker. Pubescence on frons convergent, with medial setae directed backward; metaventral setae slightly shorter than proventral setae, becoming longer anteriorly; pubescence on abdominal tergites IV–VII convergent; that on sternites IV–VII with few longer setae posteromedially, but apparently lacking macrosetae. Frons and vertex finely granulate; pronotum and elytra granulo-fossulate; prohypomera almost smooth; metaventrite coarsely punctate laterally, almost smooth in middle.

Frons above clypeus forming sharp ridge, the latter not carinate; mesal portion of disc weakly convex in lateral view, evenly; U-shaped frontal impression shallow. Temples abruptly narrowed just behind eyes, almost smooth. Occipital ridge indistinct. Antenna ( Fig. 25 ) with scape rather conical, not compressed; short and dense pubescence present only on antennomeres 5–11; antennomere 11 evenly expanded on basal two-thirds and apically rounded, slightly compressed. Pronotum ( Fig. 27 ) with hypomera lacking transverse ridge. Scutellum with anterior margin rounded. Elytral disc without notable relief.

Male. Frontoclypeal area, protarsomeres 5, metaventrite and abdominal sternites 4–6 unmodified. Protarsomeres 1 possessing ventral patch of modified adhesive setae. Metatarsomere 1 about 1.3 times as long as combined length of metatarsomeres 2–4. Peg-like setae absent from protrochanters, metatrochanters and metafemora; arranged disjunctly in 1–2 rows on protibiae ( Figs. 16–17 ); grouped in a field on mesotrochanters ( Figs. 12–13 ); arranged in two rows on mesotibiae ( Figs. 18–19 ); arranged a in single row on metatibiae, the latter prolonged apically by cluster of long setae ( Fig. 20 ). Abdominal tergite VIII as in Figs. 7, 10 ; sternite VIII as in Fig. 11 ; hemitergites IX as in Fig. 15 ; sternite IX without subbasal medial protuberance. Aedeagus as in Figs. 5–6, 8–9 .

Female. Abdominal tergite VIII ( Figs. 28–29 ) without medioapical projection; sternite VIII as in Fig. 26 . Genitalia ( Figs. 22–24 ) with membranose dorsal part of genital segment slightly sclerotized in middle and dark yellow; gonocoxal plate without dorsal or ventral medial ridges.

Comparisons and diagnostic notes. Megarthrus chujiao and M. antennalis ( Figs. 1–2 ) are the only members of the genus to have the metatibia prolonged apically by a cluster of long seta in the male. They are also the only Oriental Megarthrus to possess protibial peg-like setae in the male. These two species can be easily distinguished by males having the shape of the aedeagal ventral wall evenly narrowed toward apex in M. chujiao while it is abruptly narrowed at base in M. antennalis , and in females by the presence in M. chujiao of a pigmented weakly sclerotized mediobasal area on the dorsal part of genital segment ( Fig. 24 ), which is absent in M. antennalis (see Cuccodoro 2003: Fig. 7e ).

Distribution and natural history. Megarthrus chujiao is endemic to the Hengduan Mountains of Sichuan and Yunnan provinces in China, where it was collected in spruce-birch forests, from sifted leaf litter, mushroom, moss and dead wood, at elevations ranging from 2100 to 2850 m a.s.l.

Etymology. The name of the new species means antenna in Chinese.

Figures

FIGURES 1–4. Megarthrus, habitus, male; Megarthrus antennalis: dorsal (1) and ventral (2) views; Megarthrus chujiao sp. n.: dorsal (3) and ventral (4) views. Scale bar=0.5 mm.

FIGURES 5–10. Megarthrus chujiao sp. n. (male): aedeagus in lateral (5, 6) and ventral (8, 9) views; abdominal tergite VIII in lateral (7) and dorsal (10) views. Scale bar=0.1 mm.

FIGURES 11–21. Megarthrus chujiao sp. n.: male, abdominal sternite VIII in ventral view (11); mesotrochanter in ventral view (12); mesofemur and mesotrochanter in lateral view (13); metafemur and metatrochanter in lateral view (14); hemitergite IX (15); protibia in lateral (16) and ventral (17) views; mesotibia in lateral (18) and ventral (19) views; metatibia in lateral (20) view; Metatarsi (21). Scale bar=0.1 mm.

FIGURES 22–29. Megarthrus chujiao sp. n.: female, genital segments, ventral part in dorsal (22) and lateral (23) views, and dorsal part (24) in ventral view; antenna (25); female abdominal sternite VIII in dorsal view (26); outline of pronotum (27); female abdominal tergite VIII in dorsal (28) and lateral (29) views. Scale bar: a, c=0.1 mm; b=0.2 mm