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 Dineutus unidentatus Aubé, 1838 ( Figs. 1G , 4D , 6A–D , 7C, 7F–G , 8A ) Material examined. THAILAND : Amnat Charoen Province : Kork Stream , Kham Khuean Kaeo Subdistrict , Chanuman District , 16°12'29.9"N 104°52'11.6"E , 188 m a.s.l. , 23.XII.2017 , leg. B. Suksai , 2 males , 2 females ( THNHM ) . Khon Kaen Province : Khon Kaen University , wastewater treatment pond 8, Nai Mueang Subdistrict , Mueang Khon Kaen District , 16°27'48.2"N 102°48'29.3"E , 169 m a.s.l. , 21.XI.2001 , leg. B. Suksai , 1 male , 1 female ( KKU ) ; Phong River , Ban Huai Sai Nang , Si Chomphu Subdistrict , Si Chomphu District , 16°52'06.5"N 102°10'58.2"E , 210 m a.s.l. , 11.II.1995 , leg. N. Sangpradub , 6 males , 8 females ( KKU ) ; Pond at Ban Kho , Ban Kho Subdistrict , Mueang Khon Kaen District , 16°34'13.9"N 102°46'53.8"E , 180 m a.s.l. , 26.XI.2016 , leg. B. Suksai , 48 males , 65 females ( KKU , THNHM ) . Krabi Province : Pond at Ban Paga Sai , Nuea Khlong Subdistrict , Nuea Khlong District , 8°02'N 99°01'E , 27 m a.s.l. , 3.VI.2005 , leg. R.W. Sites , A. Vitheepradit & T. Prommi , L-828, 1 male ( UMC ) . Mukdahan Province : Huai Lao Waterfall , Ban Kho Subdistrict , Khamcha-I District , 16°44'36.9"N 104°21'04.7"E , 226 m a.s.l. , 22.XII.2017 , leg. B. Suksai , 1 male , 1 female ( THNHM ) ; Tadton Waterfall , Non Yang Subdistrict , Nong Sung District , 16°29'40.2"N 104°18'47.6"E , 208 m a.s.l. , 22.XII.2017 , leg. B. Suksai , 1 male , 2 females ( THNHM ) . Nakhon Ratchasima Province : Sakaerat Environmental Research Station , Boa yaepun, U-dom Sap Subdistrict , Wang Nam Khiao District , 14°27'56.9"N 101°54'11.7"E , 392 m a.s.l. , 26.X.2013 , leg. B. Suksai , 1 male ( KKU ) ; same locality except for, Bon weir, U-dom Sap Subdistrict , Wang Nam Khiao District , 14°29'49.2"N 101°54'55.5"E , 472 m a.s.l. , 27.III.2018 , leg. P. Chanteenok , 5 males , 6 females ( THNHM ) ; same locality except for, 29.III.2018 , leg. P. Chanteenok , 4 males , 6 females ( THNHM ) ; same locality except for, 8.IV.2018 , leg. B. Suksai , O. Pornsophon , T. Jantaranakee & S. Phengsalung , 1 male ( KKU ) . Phetchabun Province : Nam Churn Stream , Kok Mon Subdistrict , Nam Nao District , 16°40'27.0"N 101°44'03.0"E , 278 m a.s.l. , 21.III.2017 , leg. B. Suksai , 2 males , 3 females ( THNHM ) . Trang Province : Sikao District , ca. 8 km N of Chao Mai Natl. Park , 7°28'09.3"N 99°20'09.5"E , 5 m a.s.l. , 9.I.2006 , leg. A. Vitheepradit & T. Prommi , mangrove, L-906, 1 female ( UMC ) . Diagnosis. Male ( Fig. 1G ): Size: 6.0– 6.7 mm . Body form narrowly oval; apex of flagellomere VI darkly colored; elytral apices truncate and straight without parasutural spines, with epipleural spines and serrations ( Figs. 1G , 6A ); lateral marginal of pronotum and elytron black; protrochanter apically with single series of few setae on ventral surface ( Fig. 4D ); profemur without sub-apicoventral tooth; protibia wedge-shaped; venter, brown to black; epipleura brown; aedeagus ( Figs. 6B–C ) with median lobe slightly longer than parameres, parallel-sided after basal fourth, strongly acuminate in apical 1/6, apex with tip rounded, straight in lateral view. Female: Similar to male except for size: 6.4–6.9 mm ; gonocoxae elongate, lateral margin rounded, apex obliquely truncate with apicolateral corner produced ( Fig. 6D ). FIGURE 6. Elytral apex, aedeagus and gonocoxae: (A–D) D. unidentatus : (A) male elytral apex, scale bar = 2 mm; (B–C) aedeagus, scale bar = 0.5 mm: (B) dorsal view; (C) lateral view; (D) gonocoxae, ventral view, scale bar = 0.5 mm; (E–G) P. marginatus : (E–F) aedeagus, scale bars = 1 mm: (E) dorsal view; (F) lateral view; (G) gonocoxae, ventral view, scale bars = 1 mm. Differential diagnosis. Dineutus unidentatus is closest to D. australis , which also occurs in Thailand . See the differential diagnosis under D. australis to distinguish between the two species. Distribution. Widely distributed in the Indian subcontinent and Southeast Asia from western India and Sri Lanka through Assam, Bangladesh , Myanmar , Thailand , Cambodia , Laos , to Vietnam and Hainan Island ( Ochs 1929 , 1930 ; Mouchamps 1949 ; Brinck 1981 ; Vazirani 1984 ; Mazzoldi 1995 ) as far south as the Malay peninsula ( Balke et al . 2004 ) and Perak Island ( Ochs 1929 ). The species has not been recorded from Singapore ( Hendrich et al . 2004 ) and historical records from Java are considered erroneous ( Brinck 1981 ). Habitat. In Sri Lanka , the species has been found in rivers, streams, ponds, water tanks, paddy fields, and a slightly brackish lagoon ( Brinck 1981 ). On Perak Island, Malaysia , the species was taken near a waterfall in a stream ( Ochs 1929 ). We found this species near the margins of a stagnant stream and in ponds where it formed rafts of many individuals ( Figs. 7C, F–G ). Discussion. We found D. unidentatus only in the northeastern and southern regions of Thailand ( Fig. 8A ). It was found at low to medium elevation ( 5–472 m a.s.l.) and co-occurred in ponds and streams with D. spinosus . It has not been found at high elevation. We suspect that it might be found in other localities in Thailand with the same habitat and elevation.