Dicharax cucullatus (Theobald, 1870)

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 cucullatus (Theobald, 1870) Figs 2 , 3 , 4A, B , 5A , 6H

Alycaeus cucullatus Theobald, 1870: 396, 397, pl. 18, fig. 2. Type locality: Shan States [Myanmar]. Hanley and Theobald 1874: 39, pl. 96, figs 1, 4; Reeve 1878: pl. 2, sp. 12; Godwin-Austen 1914: 407, pl. 155, fig. 5; Tarruella and Domènech 2011: 72.

Alycaeus (Charax) cucullatus - Kobelt and Möllendorff 1897: 150.

Alycaeus davisi Godwin-Austen, 1914: 408, pl. 148, fig. 9, 9a. Type locality: Siam and Shan State boundary. New synonym.

Alycaeus (Dicharax) cucullatus - Kobelt 1902: 367, 368; Gude 1921: 244, 245.

Alycaeus (Chamalycaeus) davisi - Gude 1921: 226.

Dicharax cucullatus - Páll-Gergely et al. 2020b: 57, 58.

Dicharax davisi - Páll-Gergely et al. 2020b: 58.

Type material examined.

Syntypes of Alycaeus cucullatus NHMUK 1888.12.4.951-952 from Shan States (2 shells; Fig. 2A ). Syntypes of Alycaeus davisi NHMUK 1903.7.1.1630 from Shan States (4 shells; Fig. 2B ).

Other material examined.

CUMZ 7421 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 (1 shell; Figs 3A , 6H ). CUMZ 5071 from Tham Ban Luang , Doi Ang Khang , Chiang Mai Province, Thailand, 19°52'13.7"N, 99°02'44.1"E, 17 Mar. 2000, coll. S. Panha, P. Tongkerd (34 shells; Figs 2C, D , 3B ). CUMZ 7422 from Siribhum Waterfall , Doi Inthanon , Chiang Mai Province, Thailand, 18°32'48.5"N, 98°30'44.0"E, 13-15 Oct. 2009, coll. C. Sutcharit (71 shells; Figs 3C , 4A, B ). CUMZ 7423 from Wachirathan Waterfall , Doi Inthanon , Chiang Mai Province, Thailand, 18°32'31.0"N, 98°35'53.8"E, 21 Jan. 2015, coll. P. Jirapatrasilp, R. Srisonchai, W. Siriwut, T. Seesamut, C. Sutcharit (10 shells; Fig. 3D ). CUMZ 7424 from Doi Inthanon , 2,000 m a.s.l, Chiang Mai Province, Thailand, 18°35'08.5"N, 98°29'03.4"E, 21 Jan. 2015, coll. P. Jirapatrasilp, R. Srisonchai, W. Siriwut, T. Seesamut, C. Sutcharit (3 shells; Fig. 3E ). CUMZ 7432 from Doi Inthanon, ~ 1,700-2,000 m a.s.l, Chiang Mai Province, Thailand, 18°35'08.5"N, 98°29'03.4"E, 5-6 Oct. 2020, coll. P. Jirapatrasilp, A. Pholyotha, W. Siriwut, N. Likhitrakarn, C. Sutcharit (6 specimens in ethanol; Fig. 5A ) .

Diagnosis.

Shell medium-sized (SH up to 3.5 mm, SW up to 5.5 mm), depressed-conical. Spire ca. 1/5 of shell height. R1 with regular, strong ribs; R2 longer than R3; R2 with 49-57 ribs. R3 with sharp swelling near aperture. Aperture round. Inner peristome with four to five indentations, always with parieto-columellar indentation, sometimes weak at basal. Outer peristome fringed, slightly reflected but not conspicuous. Umbilicus round. Operculum multispiral with elevated lamella.

Distribution.

Shan State, Myanmar ( Gude 1921), and Chiang Mai Province, Thailand.

Remarks.

This species was originally described from Shan State and diagnosed by its fringed peristome with five indentations ( Theobald 1870). Later, Godwin-Austen (1914) described Alycaeus davisi with a less fringed peristome with four indentations from Siam and Shan State boundary. Upon examining the type specimens, both species agree in having a depressed-conical shell shape, a long R2 and a sharp swelling of R3 near the aperture (Fig. 2A, B ). The types of A. cucullatus differ from those of A. davisi in having a more fringed peristome and more indentations. However, based on recently collected specimens, we conclude that this variation is to be interpreted as intraspecific as we found that this crenulation may vary even within the same population from nearly smooth (Fig. 4A ) via slight (Fig. 4B ) to strong (Fig. 2C, D ). Because both species were described from the same geographical region, Alycaeus davisi is herein regarded as a junior subjective synonym of Alycaeus cucullatus . Refer to Discussion regarding the color of living specimen and variation in spiral striation.

Dicharax cucullatus differs from other species with similar shell shape and fringed peristome, i.e. D. anthostoma ( Möllendorff, 1885) ( Páll-Gergely et al. 2017: fig. 19a, b) from China, D. ataranensis (Godwin-Austen, 1914) ( Páll-Gergely et al. 2020b: figs 11, 12) from Myanmar and D. fimbriatus ( Páll-Gergely et al. 2017: figs 35-37) from China and Vietnam in possessing a sharp swelling nearer to the aperture. In addition, D. cucullatus differs from D. anthostoma in having shorter distance between the inner and outer peristomes and from D. ataranensis in possessing a shorter R3. Although D. tangmaiensis (Chen & Zhang, 2001) ( Páll-Gergely et al. 2020b: fig. 14) from Tongmai Town, Bomi County, Tibet Autonomous Region, China is very similar to D. cucullatus , the distance between both species’ type localities is approximately 1,100 km. Thus, the status of D. tangmaiensis needs further scrutiny.

Some specimens from Doi Inthanon possess a more depressed shell with a lower spire, a very low swelling of R3 and a nearly smooth inner peristome (Fig. 4A ) very similar to D. borealis sp. nov. However, D. cucullatus could be distinguished from D. borealis sp. nov. by a round aperture and always having a parieto-columellar indentation.

Figures

Figure 2. Dicharax cucullatus A. Syntype of Alycaeus cucullatus, NHMUK 1888.12.4.951; B. Syntype of Alycaeus davisi, NHMUK 1903.7.1.1630; C, D. Specimens CUMZ 5071 from Tham Ban Luang, Doi Ang Khang, Chiang Mai Province. Close-up images of the aperture not to scale. Photo: NHM (A, B.).

Figure 3. Dicharax cucullatus from Chiang Mai Province A. Specimen CUMZ 7421 from Doi Chiang Dao; B. Specimen CUMZ 5071 from Tham Ban Luang, Doi Ang Khang; C. Specimen CUMZ 7422 from Siribhum Waterfall, Doi Inthanon; D. Specimen CUMZ 7423 from Wachirathan Waterfall, Doi Inthanon; E. Specimen CUMZ 7424 from Doi Inthanon, 2000 m a. s. l. Close-up images of the aperture not to scale.

Figure 4. A, B. Dicharax cucullatus, specimens CUMZ 7422 from Siribhum Waterfall, Doi Inthanon, Chiang Mai Province; A. With operculum; C, D. Dicharax notus C. Syntype NHMUK 1903.7.1.3065; D. Specimen CUMZ 7425 from Tham Luang Sa Koen, Nan Province. Close-up images of the aperture not to scale. Photo: NHM (C.).

Figure 5. Living Dicharax specimens. A. Dicharax cucullatus, specimen CUMZ 7432 from Doi Inthanon, Chiang Mai Province; B. Dicharax notus, specimen CUMZ 7425 from Tham Luang Sa Koen, Nan Province. Both photographed in the laboratory. Not to scale. Photo: A. Pholyotha.

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.