( Figs 2, 6)
Stactobia biramosa Martynov 1929, 297, male, Russia (Siberia); Arefina et al. 2002, 104–105, male, female, Russia (Khavarovsk, Primorye); Arefina & Armitage 2003, 17, Russia ( Sakhalin); Chuluunbat et al. 2016, 102, Mongolia ( Arkhangai); Potikha & Vshivkova 2016, 364, Russian Far East (Primorye); Zasypkina 2016, 486, Russian Far East (Magadan); Zhou et al. 2016, 213, 214, male, China (Hei-long-jiang).
Revised description. Adult. Wings brown, some light brown patterning in forewings, but often indistinct in alcohol; light brown dots absent in hind wings. Wing length: males (n=3), forewings each 2.1–2.2 mm and hind wings each 1.9–2.0 mm; females (n=3), forewings each 2.3–2.4 mm and hind wings each 2.0– 2.1 mm. Antennae brown; in male (n=3), each 18-segmented, 1.2–1.4 mm long; in female (n=3), each 18-segmented, 0.9–1.0 mm long. Short ventral process on abdominal segment VII in male and on VI in female.
Male ( Figs 2 A–2C). Segment IX smaller than segment VIII, with pair of long anterior apodemes. Segment X membranous, subquadrate with median shallow depression apically. Subgenital plate undeveloped. Inferior appendages complex; each divided into ventral and dorsal branches at base; ventral branch short and leaf-like with many long setae in ventral view; dorsal branch gently curved dorsad, divided into long inner bar and relatively short outer bar at half length; very short ventral spine near middle of dorsal branch.Aedeagus almost straight, subacute apically, paramere absent.
Female ( Figs 2D, 2E). Tergite and sternite of segment VII fused laterally. Segments VIII–X without any surface sclerites. Segment VIII with about 15 marginal setae. Vaginal apparatus long, lozenge-shaped in ventral view, humped medially in lateral view.
Specimens examined. Russia, south-central Sakhalin: 33 males, 4 females, Lyotaga River Valley, 34 km from Yuzuno-Saknal, 25.vii.2001, B. Martin & N. Minakawa. Japan, Hokkaido: 43 males, 36 females, Obira-cho, Obirashibe-gawa, Akai-zawa, 7.vii.2007, T. Ito, net sweeping; 13 males, 12 females, same locality, 7.vii.2007, N, Kuhara (deposited in personal collection of N. Kuhara); 26 males, 24 females, same locality, 7.vii.2008, T. Ito, net sweeping.
Remarks. This species is distinguished from congeners by the complex form of the inferior appendages. The Japanese specimens concur with drawings of Russian Far Eastern specimens ( Arefina et al. 2002) and those of northern Chinese ( Zhou et al. 2016), apart from the fact that 1) the pair of darkened bars within tergite X are not obvious (clearly observed in the Russian specimens, 2) the ventral spine on the lateral margin of each inferior appendage is present (absent in the Chinese specimens).
Distribution ( Fig. 6). Russia (Siberia, Khavarovsk, Primorye, Magadan), China (Hei-long-jiang), Mongolia ( Arkhangai), Japan ( Hokkaido). New to Japan.
Habitat. Adults of this species were collected beside small streams.
Japanese name. Kita-sawa-himetobikera (newly given here).