A review of Thysanarthria with description of seven new species and comments on its relationship to Chaetarthria (Hydrophilidae: Chaetarthriini) Author Fikáček, Martin Department of Entomology, National Museum, Cirkusová 1740, CZ- 19100 Praha 9 – Horní Počernice, Czech Republic & Department of Zoology, Faculty of Science, Charles University, Viničná 7, CZ- 12844 Praha 2, Czech Republic mfikacek@gmail.com Author Liu, Hsing-Che Department of Environmental Engineering and Management, Chaoyang University of Technology, No. 168, Jifeng E. Rd., Taichung City 413, Taiwan td965771@gmail.com text Acta Entomologica Musei Nationalis Pragae 2019 2019-06-20 59 1 229 252 journal article 8143 10.2478/aemnp-2019-0020 a03ecce2-b526-4f94-aa65-620016956099 1804-6487 4488918 9F309FCC-A2ED-47B9-BC37-D0C4A3B482E5 Thysanarthria siamensis Hebauer, 2001 ( Figs 1C , 9 F–J, 11 ) Thysanarthria siamensis Hebauer, 2001: 399 . Type material examined. HOLOTYPE : ♂ ( NHMW ), THAILAND : MAE HONG SON : ʻN-THAILAND 1993 / Mae Hong Son env. / Ban Huai Po 24-30.VI. / leg. Schneider’ . Additional material examined. 1 ♂, 5 spec. ( NHMW , NMPC ): INDIA: UTTARKHAND: Gauri (str.), Pauri Garhwal, left tributary of River Alaknanda, ca. 2 km upstream from Thamdar, along road to Marud, ca. 8 km from Srinagar, 730 m , 11.xi.2006 , lgt. M. A. Jäch; 1 ♂, 2 spec. ( NHMW ):River Suhma, Dehradun district, right tributary of river Ganga, ca. 5 km S Raiwala, ca. 10 km N Haridwar, 340 m , 9.ix.2006 , lgt. M. A. Jäch. NEPAL : 1 ♂, 3 spec. ( NHMW ): Gorkha, 26.–31.v.1992 , lgt. Ivo Jeniš. LAOS : VIENTIANE : 1 ♂ , 2 spec. ( NHMB ): Laos , Vientiane , Vang-Vieng , 300, 102.4486, 18.92306, 10.v.2001 – 6.vii.2001 , J. Kolibáč . THAILAND : MAE HONG SON: 1 ♂, 2 spec. ( NHMW ): Huai Sua Tao, 11–17.v.1992 , lgt. Jan Strnad. Redescription. Body length 1.7–2.0 mm ( holotype 1.8 mm ), maximum body width 1.0– 1.2 mm ( holotype 1.0 mm). Head and labrum black; pronotum uniformly yellowish or brown centrally and gradually getting paler towards margins; elytra uniformly yellowish to pale brown, with slightly darkened striae; legs yellowish. Head without microsculpture on interstices; punctation sparse, each puncture bearing yellowish pointed seta. Eyes separated by 3.1× the width of one eye in dorsal view. Pronotum with sparse setiferous punctation similar to that on head; interstices without microsculpture. Elytra with 10 striae sharply impressed except anteromedially (near scutellar shield) where neither striae nor serial punctures are visible; intervals weakly convex at midlength and near apex; interval punctation sparse, setiferous; interstices without microsculpture. Aedeagus ( Figs 9 F–J) 0.7 mm long. Phallobase widened in apical half, widest shortly below bases of parameres (slightly wider than parameres combined); weakly arcuate in lateral view. Parameres short, narrowly elongate, constricted at midlength, widened into rounded lobes apically; widely triangular in lateral view. Median lobe narrow, shorter than parameres, sharply pointed, without membranous apex of paired subapical lobes; gonopore circular, situated subapically. Differential diagnosis. Thysanarthria siamensis is very characteristic by a relatively large aedeagus with lanceolate parameres and sharply pointed median lobe and is hence hard to be confused with any other species of the genus. Biology. Specimens from India : Uttarkhand were collected at the sides of small to large stony rivers, microhabitat is unknown (M. A. Jäch, pers. comm.). Distribution. The species is widespread, ranging from western Himalaya to central Thailand and northern Laos .