Lathrobium descendens, Assing, 2014

Assing, Volker, 2014, New species and records of Lathrobium from the Palaearctic region, primarily from Nepal (Coleoptera: Staphylinidae: Paederinae), Beiträge Zur Entomologie = Contributions to Entomology 64 (1), pp. 1-28 : 6-8

Lathrobium descendens sp. n.

( Figs 16–24 , Map 1 )

Type material: Holotype : “ NEPAL, Prov. Karnali, distr. Jumla, N Khari Lagna, Bachtal, Ufer , 3280 m NN, 29°22,14'N, 82°09,17'E, 21.VI.1999, leg. M. Hartmann / Holotypus  Lathrobium descendens sp. n., det. V. Assing 2013” ( NME).

Paratypes: 1 , 5 : same data as holotype ( NME, cAss); 1 : “ NEPAL oc. Karnali Prov., 34 km NE Jumla, Bachtal SE Taka, 29°30'12"N, 82°24'20"E, 3800 m, 01.VII.1999 leg. A. Weigel ” (cAss); 1 : “ NEPAL oc. Prov. Karnali Distr. Jumla , 15 km N Talphi Dhauli Lake 28. VI .1997 SF, HF, 4400 m leg. A. Weigel ” ( NME) .

Etymology: The specific epithet is the present participle of the Latin verb descendere (to climb down). It alludes to fact that this is the first species of the L. deuvei group to be recorded from elevations below 4000 m.

Description: Body length 5.4–6.3 mm; length of forebody 3.0– 3.2 mm. Body slender and somewhat flattened; habitus as in Fig. 16 . Coloration: whole body, including the appendages, reddish.

Head ( Fig. 17 ) 1.02–1.08 times as long as broad, weakly convex in cross section; punctation rather dense and moderately coarse; interstices on average approximately as broad as diameter of punctures, with shallow microreticulation. Eyes reduced to minute narrowly oblong rudiments without pigmentation and with approximately 5 ommatidia. Antenna long and slender, 1.9–2.1 mm long.

Pronotum ( Fig. 17 ) weakly convex in cross-section and conspicuously slender, 1.4 times as long as broad and 0.80–0.85 times as broad as head, widest anteriorly; lateral margins very weakly converging posteriorly and nearly straight in dorsal view; punctation similar to that of head; midline moderately broadly impunctate; interstices without microsculpture.

Elytra ( Fig. 17 ) slender, approximately 0.62 times as long as pronotum, combined width only approximately 1.3 times the length of suture; humeral angles completely obsolete; suture gaping posteriorly; punctation very shallow and ill-defined; interstices without distinct microsculpture. Hind wings completely reduced. Protarsomeres I–IV without appreciable sexual dimorphism, weakly dilated in both sexes.

Abdomen approximately 1.15 times as broad as elytra; punctation fine and dense; interstices with shallow microsculpture; posterior margin of tergite VII without palisade fringe; posterior margin of tergite VIII truncate to weakly convex in both sexes.

: sternite VII ( Fig. 18 ) strongly transverse and with unmodified pubescence, posterior margin broadly concave, in the middle weakly convex; sternite VIII ( Fig. 19 ) transverse, approximately 1.25 times as broad as long, in the middle with narrow band without pubescence, posterior excision approximately 0.2 times as deep as length of sternite; aedeagus ( Figs 20–22 ) 0.73– 0.77 mm long; dorsal plate with very long, distinctly sclerotized, and apically hooked apical portion, and with short membranous basal portion; internal sac with a pair of apically acute, weakly sclerotized apical structures.

: sternite VIII ( Fig. 23 ) approximately as long as broad and with convex posterior margin; tergite IX ( Fig. 24 ) undivided in the middle, postero-lateral processes apically acute and rather short, but distinctly extending beyond apex of tergite X; tergite X ( Fig. 24 ) weakly convex in cross-section, of oval shape, and slightly shorter than antero-median portion of tergite IX.

Intraspecific variation: The aedeagus of the male from the locality to the southeast of Taka ( Fig. 20 ) is distinguished from those of the males from the type locality ( Fig. 21 ) by a slightly different shape of the ventral process (lateral view). However, since no additional characters were found suggesting that the specimens from the two localities should represent distinct species, this difference is attributed to intra- rather than interspecific variation.

Comparative notes: Based on the external (slender habitus with long legs and antennae; flattened body; eyes reduced to minute rudiments; relatively long and slender elytra) and the male sexual characters (strongly transverse male sternite VII; aedeagus slender; dorsal plate with long, distinctly sclerotized, and apically hooked apical portion; presence of pairs of apical internal structures), L. descendens undoubtedly belongs to the L. deuvei group, which is distributed in West and Central Nepal ( ASSING 2012). From the previously described species of this group, L. descendens is readily distinguished by its distinctly smaller size, by the posteriorly less strongly excavate male sternite VII, the much smaller and narrower posterior excision of the male sternite VII, as well as by the shape of the smaller aedeagus. It is separated from L. barthei COIFFAIT 1987 , the sole previously known representative of the L. deuvei group recorded from West Nepal, by much smaller size alone ( L. barthei : body length 8.2 mm; length of forebody 4.3 mm). For illustrations of the previously described representatives of the L. deuvei group see ASSING (2012).

Distribution and natural history: The species was found in three localities in Jumla District, West Nepal ( Map 1 ), at altitudes of 3280–4400 m. The only record from above 3800 m, however, is based on a female and requires confirmation. The previously described species of the L. deuvei group were recorded at elevations between 4100 and 5200 m.

Figures

Map 1: Distributions of Lathrobium species in Nepal: L. semicirculatum (white triangles), L. constrictum (black triangle), L. descendens (white circles), L. ascendens (black circle), L. rude (white star), L. latibasale (black star), L. eques (white diamond), L. equitans (black diamond), L. abruptum (black square), L. kemum (white square).

Figs 16–29: Lathrobium descendens sp. n. (16–24) and L. ascendens sp. n. (25–29): habitus (16, 25); forebody (17, 26); male sternite VII (18); male sternite VIII (19, 27); aedeagus in lateral and in ventral view (20–22, 28–29); female sternite VIII (23); female tergites IX–X (24). Scale bars: 16–17, 25–26: 1.0 mm; 18–24, 27–29: 0.5 mm.