The operculate micro land snail genus Dicharax Kobelt & Moellendorff, 1900 (Caenogastropoda, Alycaeidae) in Thailand, with description of new species Author Jirapatrasilp, Parin https://orcid.org/0000-0002-5591-6724 Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Author Pall-Gergely, Barna https://orcid.org/0000-0002-6167-7221 Plant Protection Institute, Centre for Agricultural Research, Herman Otto ut 15, H- 1022 Budapest, Hungary Author Sutcharit, Chirasak Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Author Tongkerd, Piyoros https://orcid.org/0000-0001-9221-9293 Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand piyorose@hotmail.com text Zoosystematics and Evolution 2021 2021-01-05 97 1 1 20 http://dx.doi.org/10.3897/zse.97.59143 journal article http://dx.doi.org/10.3897/zse.97.59143 1860-0743-1-1 1D5553BA24894F2C9527B7E46B9B432B BD006A3AD2C6516AB596CDA05E0F375D Dicharax burchi Jirapatrasilp & Pall-Gergely sp. nov. Figs 6F , 10 , 11A Type material. Holotype CUMZ 7428/1 (Fig. 10A ), paratypes CUMZ 7428/2 (1 shell and 6 specimens in ethanol; Fig. 6F ), HNHM (1 shell), NHMUK 20200326 (2 shells) and SMF (2 shells) from Tham Phaya Nakharat, Khon Kaen Province, Thailand, 16°48'32.8"N , 101°57'23.9"E , 21 July 2020, coll. P. Tongkerd, A. Pholyotha. Figure 10. Dicharax burchi sp. nov. A. Holotype CUMZ 7428/1 with operculum; B, C. Specimen CUMZ 7431 from Doi Chiang Dao, Chiang Mai Province; D. Specimen UF 345622 from 10.2 km WNW of Soppong, Road 1095, Mae Hong Son Province. Close-up images of the aperture not to scale. Other material examined. UF 347279 from limestone pass 10.0 km NW Ban Soppong , Mae Hong Son Province , Thailand , 19°33.183'N , 98°11.533'E , 800 m a.s.l. , 23 Jun. 1987 , coll. F.G. Thompson (1 shell; Fig. 10D ) . UF 345622 from 10.2 km WNW of Soppong , Road 1095, Mae Hong Son Province , Thailand , 19°33'N , 98°03'E , 820 m a.s.l. , 20 Mar. 1988 , coll. K. Auffenberg (3 shells). HA (locality code: 2018/41) from Hsihseng centre E ca. 6 km , right side of rd. + 500 m on unpaved rd., limestone hill, Shan State, Myanmar , 20°8.002'N , 97°18.024'E , 1000 m a.s.l. , 7 Oct. 2018 , coll. A. Hunyadi, K . Okubo, J.U . Otani (1 shell; Fig. 11A ). CUMZ 7431 from Doi Chiang Dao , Chiang Mai Province , Thailand , 19°14'26.7"N , 98°52'49.8"E , 24-28 May 1997 , coll. S. Panha, J.B . Burch, P . Dumrongrojwattana (4 shells; Fig. 10B, C ) . Diagnosis. Shell small (SH up to 3.6 mm, SW up to 3.5 mm), conical. Spire ca. 1/2 of shell height. R1 with regular, strong ribs; R2 as long as R3; R2 with 36-43 ribs. R3 with either sharp and narrow or blunt and more elongated swelling in the middle of R3 or near aperture. Aperture round. Inner peristome blunt, slightly protruding. Outer peristome expanded (most conspicuously at the upper palatal position and near the umbilicus), reflected. Umbilicus partly or entirely covered by expanded outer peristome. Operculum multispiral. Description. Shell small (SH up to 3.6 mm, SW up to 3.5 mm), conical, solid, semitransparent, yellowish to pale orange. Shell outline round in apical view, spire ca. 1/2 of shell height. Whorls approaching 5, last whorl large. Protoconch low, ca. two whorls, glossy and smooth. R1 ca. 2 whorls, with regular, strong ribs; with ca. 21 ribs in 1/4 whorl adjoining R2, ribs sharper near suture and flatter near umbilicus, most prominent when approaching R2. Boundary between R1 and R2 distinct as R2 contains more close-set ribs than R1; R2 with 36-43 ribs that are curved towards aperture; R2 ca. 1/4 whorl, as long as R3. Boundary between R2 and R3 distinct due to shallow constriction; R3 smooth with indistinct growth lines; with either sharp and narrow or blunt and more elongated swelling in the middle of R3 or near aperture. Aperture round; slightly oblique to shell axis. Peristome double with prominent outer peristome. Inner peristome blunt, slightly protruding. Outer peristome strongly thickened, expanded, reflected, most conspicuously at the upper palatal position and near the umbilicus, multilayered (visible in lateral view). Umbilicus is partly or entirely closed by the reflected outer peristome. Operculum thin; multispiral ridges not significantly elevated. Etymology. In honor of Prof. John B. Burch, a prominent American malacologist, who, together with Prof. S. Panha, extensively studied the taxonomy and systematics of micro land snails of Thailand. Distribution. The new species is known from the type locality, Tham Phaya Nakharat, Khon Kaen Province, Northeastern Thailand. The other localities are Doi Chiang Dao, Chiang Mai Province and Ban Soppong, Mae Hong Son Province, Northern Thailand, and also from Shan State, Myanmar. Remarks. Differs from D. vestitus (Blanford, 1862) from Moditoung [Modi Taung, Arakan Hills] (Fig. 11B ), and its subspecies D. v. akyabensis (Godwin-Austen, 1914) from Baumi, Akyab [Sittwe] (Fig. 11C ), both from Rhakhine State, Myanmar, by having a smaller shell with a higher spire, a longer last whorl and a less distinct and a narrower constriction between R2 and R3. Differs from D. conicus (Godwin-Austen, 1871) from Samiamri, E of the Kopili R., Assam State, India (Fig. 11D ) in having a longer last whorl, more close-set ribs on R2, and the inner and outer peristomes are narrower and less reflected. Differs from D. imitator Pall-Gergely & Hunyadi in Pall-Gergely et al., 2017 from Guangxi, China in having a less smooth R1, a much thicker peristome, a longer R2, a shallower constriction between R2 and R3, the last whorl less oblique compared to the columellar axis and a less triangular aperture ( Pall-Gergely et al. 2017 ). Figure 11. A. Dicharax burchi sp. nov., specimen HA (locality code: 2018/41) from Hsihseng centre E ca. 6 km, limestone hill, Shan State, Myanmar; B. Dicharax vestitus , holotype NHMUK 1906.4.4.53; C. Dicharax vestitus akyabensis , syntype NHMUK 1888.12.4.251-252; D. Dicharax conicus , syntype NHMUK 1903.7.1.2674. Photo: NHM ( B-D ). This species exhibits the variation of R1 sculpture from nearly smooth (Fig. 10A ) to distinctly ribbed (Fig. 10C, D ) and R3 swelling from sharp (Fig. 10B, C ) to blunter and longer by having the anterior slope of swelling steeper than posterior slope (Fig. 10D ). In addition, the umbilicus is open, or covered by the reflected outer peristome. The latter trait even shows variation within the same population (maybe also depends on the age of the examined specimens).