Ischnosoma abstrusum sp. n.

Figs 19, 27, 30–32, 52, 59.

Description. Body (Fig. 27) dark brownish, head blackish, anterior margin of pronotum, humeral spot, posterior margin of elytra, posterior margins of tergites, legs, palpi and first two antennomeres brownish-yellow. Pronotum, elytra, and abdomen with distinct bluish hue.

Head 0.56–0.61 mm broad; 0.56–0.59 times as broad as pronotum, slightly broader than long. Eyes big, more than twice as long as temples. Temples behind eyes parallel. Surface smooth without microsculpture. Antenna relatively fine, 1.44–1.74 mm long. Antennomere X slightly longer than broad.

Pronotum 0.96–1.1 mm broad; 0.75–0.92 mm long; 1.15–1.23 times as broad as long, broadest in posterior third. Surface with very fine transverse microsculpture, finely and sparsely punctate.

Elytra slightly widened posteriad; along suture 0.98–1.18 mm long; 1.17–1.26 times as broad as pronotum; 1.19–1.30 times as long as pronotum. Surface with very fine transverse microsculpture. Sutural row with 12–16 punctures, discal row with 11–17 punctures and lateral row with 12–17 punctures. Wings fully developed.

Abdomen gradually tapering towards apex, sparsely puntate. Tergite VII with palisade fringe. Surface smooth with very fine microsculpture.

Length of forebody 2.9 mm; total body length 5.0– 5.6 mm.

Male. Sternite VII in the middle of posterior margin deeply concave, with area of very dense thin setae (Fig. 30). Sternite VIII with relatively long areas of palisade and beard-like setae forming six rows, and with median area of very dense setae (Fig. 31). Paramere and aedeagus: Fig. 32.

Etymology. The specific epithet (Latin adjective: hidden, secret, concealed) alludes to the impossibility to distinguish this species from it's relatives based only on habitus characters.

Type material. Holotype, male: " CHINA: Yunnan, Lincang Pref., Xue Shan, 48 km N Lincang, 2070 m, 24°19'03''N, 100°07'13''E, forest remnant, N-slope, litter & mushrooms sifted, 12.IX.2009, leg. M. Schülke [CH 09- 45] / Sammlung M. Schülke, Berlin" (cSch).

Paratypes (22): " CHINA: Yunnan, Lincang Pref., Bangma Shan, E pass, 17 km NW Lincang, 23°57'31''N, 99°56'13''E, 2040 m, secondary pine forest, litter, dead wood & mushrooms sifted, 9.IX.2009, leg. M.Schülke (CH 09-36) / Sammlung M. Schülke, Berlin", 1 ex. (cSch); " CHINA: Yunnan (CH 07-19) Dehong Dai Aut. Pref., mountain range 31 km E Luxi, 2280 m, 24°29'31''N, 98°52'58''E, secnd. pine forest with old decid. Trees, litter sifted, 3.VI.2007, A. Pütz", 1 ex. (cPüt); "P.R. CHINA, Sichuan, Emei Shan, N 29°33.6' E 103°20.6', 27.VI.–5.VII.2009, 1800–2400 m, sifting 11–17, V.Grebennikov", 1 ex. (CNC); " CHINA [6]—Yunnan, NE Kunming, 25°08'35''N, 102°53'49''E, 2320 m, mixed forest sifted, 13.VIII.2014, V. Assing", 2 exs. (cAss, cKoc); " CHINA [10]—Yunnan mt. NW Wuding, mixed forest, 25°36'53''N, 102°18'59''E, 2190 m, 17.VIII.2014, V. Assing", 1 ex. (cAss); " CHINA [11]—Yunnan, Wuding, Lion Mountain, 2200 m, 25°31'59''N, 102°22'36''E, sifted, 17.VIII.2014, V. Assing", 1 ex. (cAss); " CHINA [9b]—Yunnan, mt. W Xundian, 2300 m, mixed for., 25°34'58''N; 103°08'42''E, sifted, 16.VIII.2014, V. Assing", 5 exs. (cAss, cSch, cKoc); " CHINA [4]—Yunnan, NE Kunming, 25°09'07''N, 102°53'46''E, 2280 m, sec. pine for. with alder 11.VIII.2014, V. Assing", 1 ex. (cSch); " CHINA [5]—Yunnan, NE Kunming, 25°08'40''N, 102'53'48''E, 2290 m, mixed forest, sifted, 11.VIII.2014, V. Assing", 1 ex. (cAss); " CHINA [9]—Yunnan, mt. W Xundian, 2300 m, mixed for., 25°34'58''N, 103°08'42''E, sifted, 15.VIII.2014, V. Assing", 1 ex. (cAss).

TAIWAN: "Tengchih (1400 m) Kaohsiung, Taiwan, 25.–30.IV.2001, Sugaya H. leg. (FIT) [flight intercept trap] / Ischnosoma spec. nov. det. M. Schülke 2002", 1 ex. (KUM); " Taiwan: Kaohsiung, Tengchih, 2100 m, 19.–23.IV.2001, leg. H. Sugaya", 4 exs. (KUM, cKoc, cSch); " Taiwan: Kaohsiung, Tengchih, 1400 m, 29–30.IV.2001, leg. H. Sugaya", 1 ex. (KUM); " Taiwan: Nantou, Tehuashe, 900 m, 4.–5.V.2001, leg. H. Sugaya", 1 ex. (KUM).

Distribution. Widely distributed from Western Yunnan and Sichuan to Taiwan (Fig. 19).

Remarks. I. abstrusum sp. n. differs from similar species of the I. pictum group by the shape of the male sternite VII (posterior margin in the middle deeply concave and bordered by a cluster of very dense modified, thin long setae. The only other species with a similarly shaped male sternite VII are I. discoidale discoidale (Sharp), I. discoidale taiwanum Kocian, and I. ruth Kocian, but these species are distinguished by smaller body size, fewer and sparser modified setae on the male sternite VII, and the different chaetotaxy of the male sternite VIII.