Dicharax burchi Jirapatrasilp & Pall-Gergely, 2021

Jirapatrasilp, Parin, Pall-Gergely, Barna, Sutcharit, Chirasak & Tongkerd, Piyoros, 2021, The operculate micro land snail genus Dicharax Kobelt & Moellendorff, 1900 (Caenogastropoda, Alycaeidae) in Thailand, with description of new species, Zoosystematics and Evolution 97 (1), pp. 1-20 : 1

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.

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. ½ 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. ½ 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 ¼ 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. ¼ 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 Páll-Gergely & Hunyadi in Páll-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 ( Páll-Gergely et al. 2017).

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).

Figures

Figure 6. Synoptic view of the eight Dicharax taxa in Thailand. A. Dicharax omissus, specimen CUMZ 7426 (gold plated); B. Dicharax pratatensis, specimen CUMZ 7427; C. Dicharax panhai sp. nov., paratype CUMZ 7429 / 2; D. Dicharax pongrati sp. nov., paratype CUMZ 7430 / 2; E. Dicharax notus, specimen CUMZ 7425; F. Dicharax burchi sp. nov., paratype CUMZ 7428 / 2; G. Dicharax borealis sp. nov., paratype CUMZ 5072 / 2; H. Dicharax cucullatus, specimen CUMZ 7421.

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.

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).