Megarthrus lanka, Cuccodoro, Giulio & Liu, Zhiping, 2016

Cuccodoro, Giulio & Liu, Zhiping, 2016, Megarthrus of southern India and Sri Lanka, with notes on their phylogenetic and biogeographical relationships (Coleoptera: Staphylinidae: Proteininae), Zootaxa 4097 (4), pp. 530-544 : 539-541

Megarthrus lanka sp. nov.

( figs 1 , 48–65 )

Specimens examined. 41: Holotype, male: SRI LANKA : Central: " Ceylan, Central, s/Talatuoya [above Talatuoya], 850–1000m, 27.i.1970, Besuchet, Löbl & Mussard, #27a [sifting leaf litter in relictual forest]" (MHNG; accession number MHNG ENTO 00008938); Paratypes, 40: same data as holotype (MHNG, 6 males and 2 females); Dickoya, 20km WSW Nuwara Eliya, Gesiebt [sifted] 28.iii.1973, leg. Benick (MHNG, 1 female; ZMHB, 1 male and 1 female); Hanguranketa, 750m, 27.i.1970, leg. Besuchet, Löbl & Mussard, #28 [ex forest leaf litter] (MHNG, 16 males and 8 females]; above Mululla, 750m, 4.ii.1970, leg. Besuchet, Löbl & Mussard #45 [sifting forest leaf litter] (MHNG, 1 male and 3 females); Kandy, 14.i.1964, leg. Mussard (MHNG, 1 male).

Description. Habitus as in fig. 1. Combined length of head, pronotum and elytra = 1.65–1.85 mm; maximal pronotal width = 0.90–1.05 mm. Body and appendages uniformly rust brown, except antennomeres 11 yellowish. Dorsal pubescence fairly uniform, sparser on elytral disc; frontal pubescence parallel, medial setae directed backward; elytral and pronotal setae slightly arcuate, recumbent; metaventral setae becoming denser anteriorly, slightly longer than prosternal setae; pubescence on abdominal tergites IV–VI parallel, uniform; that on sternites IV–VII becoming slightly longer posteromedially, lacking subapical macrosetae. Surface of frons and vertex oblongogranulate; pronotum granulofossulate; anterior portion of prohypomera almost smooth; elytra punctate, coarsely; metaventrite coarsely punctate laterally, smooth medially and posteriorly.

Frons above clypeus forming sharp ridge, the latter slightly carinate, evenly or slightly higher laterally than in middle, with lateral outlines oblique to anterior portion broadly rounded, or subtruncate; mesal portion of disc weakly convex in lateral view, evenly; entire U-shaped frontal impression shallow. Eyes almost hemispherical, with highest point slightly above level of vertex; supraocular margins sinuate in dorsal view. Temples almost smooth; in dorsal view abruptly angled just behind eyes, then weakly convex. Occipital ridge well marked, darkened; anterolateral portions sinuate, extended from lower eye margins dorsally to nearly third of neck width, then sharply recurved posteroventrally back to upper level of eyes; posterolateral portions connected dorsally with irregular transverse ridge. Antenna (fig. 63) without patches of sensilla; scape gradually expanded, conical, not flattened and without longitudinal riges; pedicel cylindrical, without longitudinal ridge; short and dense pubescence present on antennomeres 8–11; antennomeres 9–10 strongly asymmetrical. Maxillary palpi with palpomere 4 about 2 times as long as palpomere 3, the latter subcylindrical.

Pronotum (fig. 61) with centre moderately convex in frontal view; disc shallowly depressed along lateral portions of anterior and posterior margins, and along lateral edges, the latter slightly raised anteriorly; medial groove very shallow, weakly arcuate in lateral view; hypomera without discal pit, at level of junction with posterior prosternal margin with short ridge, the latter arcuate outward, anterior portion not reaching half of hypomeral width and posterior portion not reaching middle of hypomeron. Proventrite with shallow posteromedial ridge. Protrochanters without longitudinal ridge. Scutellum with anterior margin of disc straight and lateral margins oblique to broadly convex apex.

Elytra with disc evenly convex, without notable relief except humeral callus obsolete and moderate depression along anterior portion of lateral edge; lateral edge arcuate in dorsal view, markedly carinate, with anterior portion shallowly serrate, broadly, serration fading posteriorly; sutural margin slightly arcuate in lateral view; posterior margin arcuate toward obtuse inner apical angle. Metaventrite without foveiform impressions in front of metacoxae. Mesofemora as long as metafemora and longer than mesotibiae, with subbasal oblique ridge; metatibiae as long as metafemora and longer than mesotibiae.

Male. Protarsomeres 1 lacking tenent setae. Protarsomeres 5 with adventral projecting flat apophysis. Metatarsomeres 1 shorter than metatarsomeres 2–4 combined. Peg-like setae arranged in single row on mesotibiae (fig. 56) and in double row on mesotrochanters (fig. 57). Abdominal sternite IV with medial area markedly swollen, with short transverse medial ridge; tergite VIII as in figs 53–54; sternite VIII as in fig 52; hemitergites IX (fig. 55) with lateral lobe reduced; sternite IX without subbasal medial protuberance. Aedeagus as in figs 48–51.

Female. Medial area of abdominal sternite IV flat. Abdominal tergite VIII as in figs 64–65; sternite VIII as in fig. 62. Genital segment as in figs 58–60; gonocoxal plate without dorsal and ventral medial ridges.

Comparisons and diagnostic notes. Megarthrus lanka sp. n. is very similar to the southern Indian M. rufomarginatus . These two species are so far the only members of the genus to possess strongly asymmetrical antennomeres nine and ten. They also uniquely share the presence on the fifth protarsomere of a flat adventral projecting apophysis in male. Megarthrus lanka is however uniformly rust brown except apical antennomere yellow, instead of chestnut brown with paler and uniformly coloured appendages for M. rufomarginatus , and the elytral punctation of the latter species is also slightly finer and denser. The shape of the aedeagus and the conformation of its internal sac are diagnostic.

Distribution and natural history. The species is known only from the Central Province of Sri Lanka , where it was collected in forest leaf litter at elevations ranging from 750 to 1000 m.a.s.l.

Etymology. The specific epithet is based on the name of the island, treated as a Latin singular noun in apposition, nominative case.

Figures

FIGURES 1 – 5. Megarthrus, habitus, male; M. lanka sp. n. (1), holotype; M. rufomarginatus Cameron (2); M. bimaculatus Fauvel (3); M. narendrani sp. n. (4), holotype; M. nilgiriensis sp. n. (5), holotype. Scale bar = 0.5 mm.

FIGURES 48 – 57. Megarthrus lanka sp. n., male; aedeagus in ventral (48, 51) and lateral (49, 50) views; abdominal sternite VIII in ventral view (52); apex of abdominal tergite 8 in dorsal (54) and lateral (53) views; right abdominal hemitergite 9 in ventral view (55); mesotibia (56); mesofemur and mesotrochanter (57). Scale bars = 0.1 mm.

FIGURES 58 – 65. Megarthrus lanka sp. n.; female genital segment, ventral part in dorsal (58) and lateral (59) views, and dorsal part (60) in ventral view; antenna (63); outline of pronotum (61); female abdominal sternite VIII in dorsal (62); female abdominal tergite 8 in dorsal (64) and lateral (65) views. Scale bar = 0.1 mm.