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 bifida sp. nov. ( Figs 6 A–E, 11 ) Type material. HOLOTYPE : 1 ♂ ( NHMW ), THAILAND : MAE HONG SON : Mae Ping , at light , 6.i.–30.ix.1991 , lgt. Malicky . PARATYPES : 6 specimens ( NHMW , NMPC ): same data as the holotype. CHIANG MAI: 2 spec. ( NHMW ): Chiang Mai , Zoo, at light , 18.–25.iv.1988 , lgt. Chantaramongkol & Malicky . SONGKHLA : 3 spec. ( NHMW ): ʻab Ton Nga Chang WF’ , 4.–5.v.1993 . Description. Body length 1.2–1.5 mm ( holotype 1.3 mm ), maximum body width 0.8–0.9 mm ( holotype 0.9 mm ). Head and labrum black, pronotum and elytra uniformly yellowish; legs reddish to yellowish. Head with weak mesh-like microsculpture on interstices; punctation sparse, each puncture bearing a seta. Eyes separated by 4.0× the width of one eye in dorsal view. Pronotum with sparse setiferous punctation similar to that on head; interstices smooth, without microsculpture. Elytra with 10 striae sharply impressed except anteromedially (near scutellar shield) where neither striae nor serial punctures are visible; intervals convex at midlength and near apex; interval punctation sparse, setiferous; interstices without microsculpture. Aedeagus 0.5 mm long. Phallobase weakly and gradually narrowing from base of parameres towards base, slightly widened basally, weakly arcuately bent in lateral view; c. 2× longer than parameres. Paremeres short, wide basally, gradually narrowing towards apex, lateral face nearly continuously arcuate, apex bluntly rounded. Median lobe wide at level of gonopore, indistinctly constricted basally of it, apex membranous, widely rounded; subapical part with two triangular membranous lobes; apex reaching c. level of apex of parameres; gonopore transversely oval, situated below bases of paired projections. Fig. 5. Male genitalia of Thysanarthria species, holotypes.A–E – T.brincki Hebauer, 2001 (A–C – whole aedeagus in dorsal, lateral and ventral view; D–E – detail of median lobe and parameres in dorsal and ventral view); F–J – T. cardamona sp. nov. (F–H – whole aedeagus in dorsal, lateral and ventral view; I–J – detail of median lobe and parameres in dorsal and ventral view); K–M – T. bengalensis Hebauer, 2001 (K – photo of the aedeagus before re-mounting; L – whole aedeagus in ventral view; M – whole aedeagus in lateral view). Differential diagnosis. Thysanarthria bifida is easy to regonize by the median lobe bearing a pair of subapical membranous projections combined with the short parameres arcuately narrowing into simply rounded apices. In these characters it closely resembles T. trifida sp. nov. from which it mainly differs in smaller body size ( 1.2–1.5 mm in T. bifida , 1.9–2.0 mm in T. trifida ), shorter and wider parameres (compare Figs 6 A–E to 6 F–J) and the membranous apex of the median lobe widely rounded (compared to the pointed one in T. trifida ). Etymology. The species name refers to the subapical pair of projections on the median lobe which make the apex of the median lobe seemingly bifid when observed under the microscope. Adjective. Biology. Most examined specimens were collected at light, no more data are available about the biology. Distribution. The species is so far known from three localities, two of which are situated in northwestern Thailand (provinces Mae Hong Son and Chiang Mai ) and the last in the southernmost Thailand close to the border with Malaysia (province Songkhla). This indicates that the species is likely quite widely distributed but overlooked and rarely collected.