The Gyrinidae (Coleoptera) fauna of Thailand: Key to tribes and genera, with new records and keys to species of Dineutini and Gyrinini Author Suksai, Benjamart 0000-0002-2472-6100 benjamartbenjamart@gmail.com Author Gustafson, Grey T. Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas 66045, USA. & Department of Biological Sciences, Northern Arizona University, Flagstaff, Arizona, 86011, USA. Author Sites, Robert W. 0000-0002-3895-813X Enns Entomology Museum, Division of Plant Science, University of Missouri-Columbia, Missouri 65211, USA. SitesR @ missouri. edu; https: // orcid. org / 0000 - 0002 - 3895 - 813 X Author Sangpradub, Narumon Applied Taxonomic Research Center, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand text Zootaxa 2021 2021-11-22 5071 1 97 117 journal article 3307 10.11646/zootaxa.5071.1.5 f5a054cf-41c7-40cd-bac9-63e1ea8d1b8e 1175-5326 5723327 C7DFE939-E932-4570-8496-7A67A51D4D7A Key to the tribes and genera of adult Gyrinidae in Thailand, including species of adult Gyrinini and Dineutini 1 Dorsal surface of pronotum and elytron with pubescence; abdominal sternite VIII narrow and long....... Orectochilini , 2 - Dorsal surface of pronotum and elytron completely glabrous ( Figs. 1A–H ); abdominal sternite VIII broad and short....... 3 2 Antenna with six flagellomeres; surface of pronotum and elytron with glabrous regions medially and pubescence marginally............................................................................................... Patrus - Antenna with nine flagellomeres; surface of pronotum and elytron without glabrous regions, entirely covered with pubescence.................................................................................... Orectochilus 3 Size smaller, length <6.0 mm; pronotum with median transverse depression; scutellum visible; elytron with 11 longitudinal striae ( Figs. 1A–B , 2A–B ).............................................................. Gyrinini , Gyrinus , 4 - Size larger, length 6.0–17.0 mm; pronotum without median transverse depression; scutellum not visible ( Figs. 1C–H ); elytron without evident longitudinal striae.............................................................. Dineutini , 5 4 Dorsally metallic in appearance lateral sides of elytra with bronzy sheen ( Fig. 1A ), intervals VI–X not sulcate............................................................................................ Gyrinus sericeolimbatus - Dorsally iridescent in appearance ( Fig. 1B ); lateral sides of elytra without bronzy sheen, intervals VI–X strongly sulcate ( Fig. 2B )............................................................................... Gyrinus smaragdinus 5 Labrum short and broad, not triangular in form ( Figs. 1C–G ); apex of protibia without spine................ Dineutus , 6 - Labrum long and triangular in form ( Fig. 1H ); apex of protibia with spine ( Fig. 1H )......... Porrorhynchus marginatus 6 Size smaller, length 6.0– 8.2 mm ; profemur of males without sub-apicoventral tooth; protibia wedge-shaped; elytral apices variously shaped........................................................................................ 7 - Size larger, length 13.4–17.0 mm; profemur of males with sub-apicoventral tooth; protibia club-shaped; elytral apices rounded ( Figs. 1E , 5F ).................................................................................. D. sitesi 7 Apex of flagellomere VI darkly colored; elytral apices without parasutural spines; lateral margin of pronotum and elytron black.............................................................................................. 8 - Apex of flagellomere VI lightly colored; elytral apices with parasutural spines ( Figs. 1F , 5J ); lateral margin of pronotum and elytron orange or yellow...................................................................... D. spinosus 8 Size smaller, length 6.0– 6.9 mm ; body form narrowly oval; elytral apices with epipleural spines ( Figs. 1G , 6A ) evident in both sexes; elytral apex truncate and straight ( Figs. 1G , 6A ); protrochanter of male apically without patch of thick setae on ventral surface ( Fig. 4D )......................................................................... D. unidentatus - Size larger, length 7.6–8.2 mm ; body form oval; elytral apices of male only with epipleural spines ( Figs. 1C , 5A ), female without epipleural spines ( Figs. 1D , 5B ); elytral apex obliquely truncate ( Figs. 1C–D , 5A–B ); protrochanter of male apically with patch of thick setae on ventral surface ( Fig. 4A ).................................................... D. australis