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 brittoni Balfour-Browne, 1951 ( Figs 4 K–O, 11 ) Thysanarthria brittoni Balfour-Browne, 1951: 215 . Thysanarthria brittoni : HEBAUER (1997: 267 , catalogue); HANSEN (1999: 105 , catalogue). Type material examined. HOLOTYPE : ♂ ( BMNH ), ʻType // W ADEN PROT / Wadi at foot of / Jebel Harir / ca. 5,000 ft / 1,2. xi.1937 // B. M. Exp. to / S. W. Arabia / H. Scott & / E. B. Britton / B. M. 1938-246 // J. Balfour-Browne det. / Thysanarthria / brittoni Type!ʼ. Redescription. Body length 1.6 mm , maximum body width 1.0 mm. Head and labrum black, pronotum and elytra uniformly yellowish; legs reddish to yellowish. Head with weak microsculpture on interstices; punctation sparse, each puncture bearing 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 with weak microsculpture. Elytra with 10 striae sharply impressed except anteromedially (near scutellar shield) where neither striae nor serial punctures are visible; interval punctation sparse, setiferous; interstices without distinct microsculpture. Aedeagus ( Figs 4 K–O) c. 0.5 mm long. Phallobase strongly widened at base of parameres, c. as wide as bases of parameres combined, strongly constricted at c. midlength, slightly bent in lateral view. Paremere widely rounded basally, slightly narrowing in apical third, apex rounded, apices divergent from each other. Median lobe narrow, membranous apically, without subapical projections; apex reaching c. level of apex of parameres; gonopore transversely oval, situated in distal third. Variability. BALFOUR- BROWNE (1951) mentions that the dorsal microsculpture of the head and pronotum, which is very weakly developed in the holotype , is stronger in some of the paratypes which are hence externally undistinguishable from T. atriceps . Differential diagnosis and discussion. Thysanarthria brittoni is very similar to T. atriceps in all characters including male genitalia, which only differ in the proportions of the parameres including their slightly diverging apices, and by the more strongly constricted phallobase (see under T. atriceps for details). The difference of the genitalia of T. brittoni from the examined specimens of T. atriceps is bigger than the observed intraspecific variability of T. atriceps , which is the reason why we consider T. brittoni a separate species at the moment. Biology. Unknown. Distribution. Only known from the type locality in western Yemen , Arabian Peninsula (BALFOUR- BROWNE 1951).