Dicharax (?) Kobelt & Mollendorff 1900
- Dataset
- Nineteen new species of Alycaeidae from Myanmar and Thailand (Gastropoda: Caenogastropoda: Cyclophoroidea)
- Rank
- GENUS
- Published in
- 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): 1-61, DOI: 10.11646/zootaxa.4973.1.1
Classification
- kingdom
- Animalia
- phylum
- Mollusca
- class
- Gastropoda
- order
- Architaenioglossa
- family
- Cyclophoridae
- genus
- Dicharax
description
Description. Shell light grey, slightly semi-translucent; shell outline rounded in dorsal view; spire slightly elevated, body whorl rounded; protoconch low, finely granular, glossy, 1.5 whorls; R 1 of 1.25 whorls, beginning with low ribs that appear curved anteriorly, developing into wide, flattened ribs separated by grooves, forming a smoothish, glossy surface; first whorl of R 1 with some fine spiral striation; boundary between R 1 and R 2 not conspicuous due to similar rib morphology, although ribs become denser, ca. 30 R 2 ribs present; R 2 + R 3 less than quarter whorl (ca. 70 – 80 ˚); R 3 considerably shorter than R 2; boundary between R 2 and R 3 distinct due to sculpture change and rather deep constriction; R 3 strongly reduced, represented only as a slight swelling just behind peristome; aperture almost parallel with shell axis, circular, round; peristome weak, very slightly thickened; boundary between inner and outer peristomes barely discernible; inner peristome weak, somewhat protruding and very slightly expanded, outer peristome very weakly developed, only indicated; umbilicus relatively narrow, less than one third of shell width. Measurements. D: 1.65 mm, H: 1.15 mm. Operculum. Unknown.
description
Fig. 22
diagnosis
Diagnosis. Tiny Dicharax species with wide, flat R 1 ribs and fine spiral striation, short R 2 with flat ribs, strongly reduced R 3, and circular aperture.
diagnosis
Differential diagnosis. The R 3 region practically absent in this species. No other low-spired alycaeid species has this trait in Thailand or Myanmar. The Dicharax species described as Awalycaeus Kuroda, 1951 in Japan also have a strongly reduced R 3, but we consider this is a case of convergent evolution.
discussion
Remarks. This species has unusual conchological characters, and therefore, its generic placement is unclear. The spiral striation on R 1 and the lack of spiral striation on the protoconch suggests a relationship to Chamalycaeus, whereas the glossy shell surface, the flattened R 2 ribs, and the low protoconch indicate a position in Dicharax. This study revealed other Dicharax species / populations that possess some spiral striae on R 1 (see under Dicharax admirandus, n. sp. and D. omissus and Páll-Gergely et al. 2017). Thus, the placement of this species in Dicharax is justified.
distribution
Distribution. This new species is known only from the type locality (Fig. 17).
etymology
Etymology. The specific epithet gnomus (Medieval Latin for gnome) refers to the tiny shell that has unusual shell area ratios compared to most other species (to be used as a noun in apposition).
materials_examined
Material examined. Holotype: Thailand, Phrae Province, 4 km N of Ban Nim Rin, valley with limestone ridges, 18 ° 10.133 ’ N, 99 ° 56.233 ’ E, 200 m a. s. l., 16 May 1988, F. G. Thompson leg., leaf litter at base of boulders, UF 380401 (D: 1.65 mm, H: 1.15 mm).