( Figs 1, 6)
Stactobia tshistjakovi Arefina & Morse in Arefina et al. 2002, 103–104, male, Russian Far East (Khasansky); Arefina & Armitage 2003, 17, Russian Far East ( Sakhalin).
Stactobiella tshistjakovi: Arefina 2004, 209; Ito et al. 2010, 57, Japan ( Hokkaido); Ito 2013, 51, 80, Japan ( Hokkaido); Potikha & Vshivkova 2016, 364, Russian Far East (Primorye); Ito 2017, 40, Japan ( Hokkaido); Ito 2018, 508, 511, Japan ( Hokkaido).
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=5), forewings each 1.8–2.0 mm and hind wings each 1.6–1.8 mm; females (n=5), forewings each 2.0– 2.2 mm and hind wings each 1.8–1.9 mm. Antennae brown; in male (n=5), each 18-segmented, 0.8–1.1 mm long; in female (n=5), each 18-segmented, 0.6–0.7 mm long. Short ventral process on abdominal segment VII in male and on VI in female.
Male ( Figs 1 A–1F). Segment IX smaller than segment VIII, with pair of long anterior apodemes. Segment X membranous, subquadrate with pair of heavily sclerotized hook-shaped rods near ventral edges internally. Subgenital plate bar-like, arising from above bases of inferior appendages, directed caudad, subacute apically. Inferior appendages narrowly triangular in ventral view, without any humps or branches, each with 4 long setae near base, curved mesad and with 2 fine setae subapically. Aedeagus divided at basal 3/5, semi-membranous at apical 1/5, beak-like apically; paramere arising at basal 3/5, directed caudad, slightly shorter than aedeagus.
Female ( Figs 1G, 1H). Tergite and sternite of segment VII fused laterally. Segments VIII–X without any surface sclerites. Segment VIII with about 20 marginal setae. Vaginal apparatus long lozenge-shaped in ventral view, mushroom-shaped in lateral view.
Specimens examined. Russia, central Sakhalin: 7 males, 12 km from Tymovskoye Town, 6.viii.2001, B. Martin & N. Minakawa. Japan, Hokkaido: 4 males, 30 females, Horokanai-cho, Shumarinai, Shumarinai-gawa, small tributary, 7.vii–3.viii.2016, T. Ito, Malaise trap & light pan trap; 6 males, 33 females, Shibecha-cho, Shirarutoro-etoro-gawa, Tomi-bashi, 25.vii.2008, T. Ito, light trap; 17 females, same locality, 16.vii.2009, T. Ito, light trap; 1 male, 5 females, same locality, 28.vii.2012, T. Ito, light trap; 10 males, 15 females, Shibecha-cho, Shirarutoro-etoro-gawa, 17 m above sea level, 16.vii.2009, T. Ito, light trap; 1 female, Eniwa-shi, Ichankoppe-zawa, 200 m above sea level, 15.vii.2000, T. Ito, light trap; 2 males, 2 females, Otaru-shi, Okusawa-suigenchi, 29.vii.1996, Y. Sasaki & F. Takahashi, (mounted on slide by N. Kuhara; deposited in personal collection of N. Kuhara); 5 males, Kuromatsunai-cho, Utasai-gawa, tributary, 100 m above sea level., 16.vii.2005, N. Kuhara (deposited in personal collection of N. Kuhara); 1 male, Nanae-cho, Onuma-choshi-guchi, 23.vi.2003, T. Ito, net sweeping. Honshu, Iwate: 1 male, Oshu-shi, Koromogawa-ku, Omori, Misawa-gawa, Tatsumi-bashi, 19.vi.2017, T. Ito, light pan trap. Shiga: 6 males, 1 female, Higashi-omi-shi, Kanzaki-gawa, Kazakoshi-dani, 29.v.2015, T. Ito, light trap.
Remarks. The male of this species is distinguished from those of congeneric species by the hook-shaped rods of segment X, the almost straight form of the subgenital plate, the narrowly triangular inferior appendages with beak-like apices and the distallybifurcate aedeagus with a straight paramere. The female is described for the first time.
Distribution ( Fig. 6). Russian Far East (Primorye, Sakhalin), Japan ( Hokkaido, Honshu). New to Honshu.
Habitat. Adults of this species were collected beside small stony streams.
Japanese name. Sawa-himetobikera.