Dicharax omissus (Godwin-Austen, 1914)

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 omissus (Godwin-Austen, 1914) Figs 6A , 8A, B

Alycaeus omissus Godwin-Austen, 1914: 411, pl. 155, fig. 13. Type locality: Siam and Shan State boundary.

Alycaeus (Chamalycaeus) omissus - Gude 1921: 231.

Dicharax (?) Dicharax omissus - Páll-Gergely et al. 2020b: 100.

Type material examined.

Syntypes NHMUK 1903.7.1.1228 from Siam & Shan boundary (2 shells; Fig. 8A ).

Other material examined.

CUMZ 7426 from Tham Mae La Na , Mae Hong Son Province, Thailand, 19°34'28.9"N, 98°12'57.4"E, 19 Jan. 2017, coll. C. Sutcharit (1 shell; Figs 6A , 8B ) .

Diagnosis.

Shell very small (SH up to 1.7 mm, SW up to 2.7 mm), depressed-conical. Spire ca. 1/4 of shell height. R1 with regular, strong ribs; R2 shorter than R3; R2 with 35-36 ribs. R3 with blunt central swelling. Aperture round. Inner peristome without indentation, with beak-like basal protrusion in newly examined population. Outer peristome expanded, not reflected. Umbilicus round.

Distribution.

Border region between Thailand and Myanmar ( Gude 1921), and Mae Hong Son Province, Thailand.

Remarks.

The specimen from Mae Hong Son Province (Fig. 8B ) exhibits stronger R1 ribs and possesses a beak-like protrusion at the base of the aperture, which is absent in the syntype (Fig. 8A ). Apart from these differences, this specimen is nearly identical to the syntype in terms of shell size and shape, and R2 and R3 length. In addition, the locality of this specimen lies only approximately 12 km from the boundary between Thailand and Shan State, Myanmar. We thus identify this specimen as D. omissus . The most similar species to D. omissus is D. notus , which is larger and has reflected outer peristome.

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 8. A, B. Dicharax omissus A. Syntype NHMUK 1903.7.1.1228; B. Specimen CUMZ 7426 from Tham Mae La Na, Mae Hong Son Province C, D. Dicharax pratatensis C. Holotype CUMZ Cy 001; D. Paratype CUMZ Cy 002 from Doi Chiang Dao, Chiang Mai Province. Close-up images of the aperture not to scale.