Dicharax subroseus Páll-Gergely, 2021

Páll-Gergely, Barna, Hunyadi, András, Grego, Jozef, Reischütz, Alexander & Auffenberg, Kurt, 2021, Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea), Zootaxa 4973 (1), pp. 1-61 : 41-43

Dicharax subroseus Páll-Gergely n. sp.

Fig. 33

Material examined. Holotype: Thailand, Surat Thani Province, limestone hill right side off km. 105.2 rd. #401 (Suratthani—Takuapa), 8°53.622’N, 98°33.179’E (locality code: Th.119.00), Ch. & J. Hemmen leg., SMF 360000 (D: 2.79 mm, H: 1.83 mm) . Paratype: 1 shell, same data as holotype, SMF 360001 .

Etymology. The specific epithet refers to the slight pinkish coloration of the available specimens.

Diagnosis. A Dicharax species with a depressed shell, slight pinkish colouration, very widely spaced ribs on the last whorl of R1, a short R2 with straight, widely-spaced ribs, and a comparatively small, rounded aperture.

Description. Shell whitish-yellowish with some pinkish colouration (holotype at the R2-R3 area, paratype on initial whorls); shell outline rounded in dorsal view; spire only slightly elevated; body whorl rounded; protoconch low, rather glossy, 1.25–1.5 whorls; R1 of 1.75–2 whorls; first whorl of R1 with only weak growth lines, gradually changing to strongly ribbed, spaces between ribs increase width rapidly (last half whorl of R1 with only 15–20 ribs); ribs straight, strong, narrow, but relatively low; boundary between R1 and R2 distinct due to denser R2 ribs; R2 with ca. 16, widely-spaced, low and rather narrow; R2+R3 approximately a quarter whorl or slightly more; R2 slightly shorter than R3; boundary between R2 and R3 conspicuous due to smooth R3 beginning and rather deep constriction; R3 with widely-spaced ribs, only anterior to constriction similar to those on R1, and blunt but prominent central swelling; aperture strongly oblique to shell axis, rounded, conspicuously small compared to shell size; boundary between inner and outer peristomes distinct; inner peristome prominent, protruding, relatively narrow; outer peristome as strong as inner peristome, strongly expanded, slightly reflected; umbilicus wide, approximately a third of shell width.

Measurements. D: 2.74–2.79 mm, H: 1.7–1.83 mm.

Operculum. The holotype possesses an operculum in the original position which appears to be separated into two layers. The outer layer, being partly broken, allows examination of the more deeply set layer. The outer surface is glossy without any surface structures. A central nipple is visible through the semi-translucent inner layer.

Differential diagnosis. The combination of small size, widely-spaced R1 ribs, and a relatively small aperture is unlike any other species in the region.

Distribution. This new species is known only from the type locality ( Fig. 3 ).

Figures

FIGURE 3. Distribution of alycaeid species in southern Thailand. Filled triangle: Dicharax ovatus Páll-Gergely & Auffenberg, n. sp., inverted filled triangle: Dicharax subroseus Páll-Gergely, n. sp., inverted empty triangles: Chamalycaeus irmatallus Páll-Gergely, n. sp., empty circles: C. krabiensis Páll-Gergely & A. Reischütz, n. sp., filled circle: Chamalycaeus serratus Páll-Gergely & Auffenberg, n. sp., empty triangles: Chamalycaeus hirpex Páll-Gergely & A. Reischütz, n. sp., filled square: Chamalycaeus buaboke Páll-Gergely & A. Reischütz, n. sp.

FIGURE 33. Dicharax subroseus Páll-Gergely, n. sp., A: holotype (SMF 360000); B: Holotype, operculum in situ; C: paratype (SMF 360001).