Megarthrus basicornis Fauvel, 1904

Liu, Zhiping & Cuccodoro, Giulio, 2020, Megarthrus of China. Part 2. Megarthrus basicornis Fauvel, 1904 with description of a new species from Mount Emei (Coleoptera: Staphylinidae: Proteininae), Zootaxa 4895 (1), pp. 124-134 : 126-128

Megarthrus basicornis Fauvel, 1904

( Figs 1-7 , 10-11 , 39 )

Megarthrus basicornis Fauvel, 1904: 87 ; Cuccodoro, 2003: 366 (redescription).

Diagnosis. For detailed morphology see Cuccodoro (2003). Habitus as in Figs 1-3 . Combined length of head, pronotum, and elytra 1.6-1.7 mm; maximal pronotal width = 0.8-0.9 mm. Body uniformly dark brown, with appendages slightly paler; antennomeres 1-4 paler than antennomeres 5-11. Dorsal pubescence uniform; pubescence on frons converging, with medial setae directed backward; metaventral setae shorter than proventral setae, fairly uniform; antenna with short and dense pubescence present only on antennomeres 5-11; abdominal pubescence converging on tergites IV-V; each sternite bearing a pair of long posteromedial setae. Frons above clypeus forming sharp ridge, the latter not carinate; temples abruptly narrowed just behind eyes, almost smooth; occipital ridge indistinct; pronotum ( Fig. 6 ) only slightly larger than elytra at base; prohypomeron punctate, lacking transverse ridge ( Fig. 7 ); elytron abruptly narrowed basally.

Male. Frontoclypeal area, protarsomere 5, metasternum and abdominal sternites IV-VI unmodified. Protarsomere 1 without ventral patch of modified adhesive setae ( Figs 10-11 ). Mesofemur about as long as metafemur. Mesotibia about as long as metatibia. Peg-like setae absent from protibia, metatrochanter and metafemur, and arranged in a single row on mesotrochanter, mesotibia, and metatibia. Aedeagus as in Figs 4-5 .

Female. Abdominal tergite VIII without medioapical projection.

Additional material examined (2 specimens). “ China, Yunnan, Dali Bai Aut. Pref., Wuliang Shan , 9km SW Weishan, 25°10’15.5’’N, 100°14’21.8’’E, 2480m, scrub with (oak, alder, pine), litter & mushrooms sifted, 14.IX.2009, leg., M. Schülke [CH09-51]”, 1 male in cSch; “ China, Yunnan, Gaoligong Shan, pass SW Baoshan, 4.-6.VI.2006, Jeniš”, 1 male in NMPC .

Distribution and natural history. The species was known so far only from in India (Himachal Pradesh, Meghalaya, and West Bengal) and Nepal (Mid-Western, Western, and Central Regions) ( Fauvel 1904, Cuccodoro 2003), and it is reported here for the first time from China (Yunnan Province) ( Fig 39 ). It occurs at elevations ranging from 1750 to 2950 m a.s.l., mainly in samples of forest leaf litter with decaying wood and fungi.

Comparisons and diagnostic notes. Megarthrus basicornis may be easily distinguished from the other Megarthrus species known so far to occur in China by its uniformly dark brown body color, in combination with the elytra abruptly narrowed basally, and the abdominal pubescence converging on tergites IV-V. Its sexual characters are also diagnostic.

This species is particularly notable because on the one hand it possesses many features found elsewhere in the genus almost exclusively in members of the M. depressus supergroup of species, such as the proventral pubescence longer than the metaventral pubescence and the presence of a pair of long posteromedial setae on each abdominal sternite in combination with the absence of a prohypomeral ridge, but on the other hand it lacks a ventral patch of modified adhesive setae on the male first protarsomere ( Figs 10-11 ), which is the only character uniquely shared by all the members of this supergroup of species. The presence of a tuft of long setae at base of the aedeagal dorsal valve is unique within the genus.

Figures

FIGURE 39. Distribution map of Megarthrus basicornis Fauvel (pink squares) and Megarthrus budai sp. n. (red circle). Scale bar =200 km.

FIGURES 1-3. Megarthrus basicornis Fauvel, habitus, male: dorsal (1), ventral (2), and lateral (3) views. Scale bar = 0.5 mm.

FIGURES 4-5. Megarthrus basicornis Fauvel, male: aedeagus in lateral (4) and ventral (5) views. Scale bar = 0.35 mm.

FIGURES 6-9. Megarthrus basicornis Fauvel (6-7) and M. budai sp. n. (8-9): prothorax in dorsal (6, 8) and ventral (7, 9) views. Scale bar = 0.2 mm.

FIGURES 10-13. Megarthrus basicornis Fauvel (10-11) and M. budai sp. n. (12-13): Portarsus of male in ventrolateral (10, 12) and ventral (11, 13) views. Ovals indicate absence (red) or presence (green) of ventral patch of modified adhesive setae (green arrows). Scale bar = 0.1 mm.