Four new species of Georissa W. Blanford, 1864 (Gastropoda, Hydrocenidae) from Thailand Author Klongklaew, Kanyaporn Department of Biology, School of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand Author Poeaim, Supattra 0000-0003-1293-3820 Department of Biology, School of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand Author Dumrongrojwattana, Pongrat Department of Biology, Faculty of Science, Burapha University, Bangsaen, Chonburi 20131, Thailand text Zoosystematics and Evolution 2024 2024-10-04 100 4 1347 1360 journal article 304167 10.3897/zse.100.128717 a7f81ef5-5178-48c8-8d40-80b29116daad FD4C02D2-01F9-4A4C-817B-F81B27F22A41 Georissa kohsichangensis Klongkaew, Poeaim & Dumrongrojwattana sp. nov. Figs 2 B , 4 E – H , 5 E – H Type material. Holotype • ZRCBUU 0902 (Fig. 2 B ). SH = 2.10 mm , SW = 1.43 mm , AH = 0.63 mm , AW = 0.90 mm , W = 4.25–4.5 . Paratype • ZRCBUU 0903 (Fig. 4 E – H ) (12 shells); Shell measurements: SH = 1.72–2.03 mm (1.86 ± 0.10 mm ), SW = 1.21–1.42 mm (1.30 ± 0.07 mm ), AH = 0.51–0.72 mm (0.62 ± 0.05 mm ), AW = 0.75–0.84 mm (0.79 ± 0.03 mm ), W = 3.75–4.5 (all type material from type locality; 30 October 2021 , P. Dumrongrojwattana leg). Type locality. Thailand , Yai Man cave , Koh Sichang district , Chonburi Province ; 13 ° 09 ' 08.2 " N , 100 ° 48 ' 28.0 " E . Etymology. This specific designation “ kohsichangensis ” is a district referring to the type locality. Diagnosis. Shell minute, ovately conical and the upper half part of the whorls is slightly downward, orangish to brownish, protoconch round to slightly ellipsoid and perforated sculpture. Body whorl with 6–7 spiral lirae. Aperture rhombate. Umbilicus closed. Operculum corneous with apophysis, paucispiral, opaque white, and rhombate. Description. Shell minute, dextral, orangish to brownish, ovately conical with 4.25–4.5 whorls (Fig. 2 B ). Protoconch orange, about one whorl, round to slightly ellipsoid, covered with perforated sculpture (Fig. 4 F, G ). Teleconch orange 3.25–3.5 whorls. The upper half part of the body whorls is slightly downward, sculptured with only strong oblique growth lines, 6–7 prominent lirae, weak oblique growth lines present on the half lower part of the body whorls, more densely spaced spiral cords, ca. 6–8 cords, at the basal part of the body whorl (Fig. 2 B , 4 E ). Suture incised. Aperture rhombate. Peristome thin, sharp, unexpanded or thickened, not reflected. Umbilicus closed. Operculum paucispiral, nucleus submarginal, corneous, opaque white, rhombate shape, thin, smooth outside surface with apophysis, inside surface with an arched peg arising from base (Fig. 4 H ). Radula. Ribbon-like, slender, longer and delicate towards the outside, rhipidoglossate (Fig. 5 E – H ). Central tooth five small teeth, trapezoid shape. Lateral teeth five teeth, claw-like with 7–11 alternately long and short denticles decreasing in size from the first lateral tooth toward the 5 th lateral tooth. Marginal teeth two teeth, claw-like with 14–18 equal size denticles. Radula formula 2: 5: 1 + 1 + 1 + 1 + 1 + 1: 5: 2. Differential diagnosis. Georissa kohsichangensis sp. nov. resembles G. carinata Sutcharit & Jirapatrasilp, 2020 from Cambodia . Georissa carinata differs in having more convex body whorl, a smooth protoconch, and sculptured with thin and uneven growth lines.