Dicharax (?) admirandus Páll-Gergely & Auffenberg 1900

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 : 21-23

Dicharax (?) admirandus Páll-Gergely & Auffenberg n. sp.

Figs 14–15

Material examined. Holotype: Thailand, Loei Province, 9.2 km NW Loei, Buddhist temple, up and N of main cave entrance, 17°35’N, 101°44’E, 250 m a.s.l., 28 Apr. 1988, K. Auffenberg leg., base of cliff under Georissa zone, UF 345861 (D: 2.9 mm, H: 1.9 mm) . Paratype: 1 shell, same data as holotype, UF 551218 .

Etymology. The specific epithet admirandus (Latin for astonishing, remarkable, extraordinary) refers to several notable shell characters of this new species, namely the strong keel, strongly fringed aperture, and the spiral striation.

Diagnosis. A medium-sized Dicharax species with strong peripheral keel, strongly ribbed and spirally striated R1, and strongly fringed aperture.

Description. Shell off-white, although both available shells were somewhat eroded; shell outline slightly oval in dorsal view; spire slightly elevated, low conical, body whorl with conspicuous peripheral keel; protoconch somewhat elevated, finely granular, spiral striation lacking, 1.75 whorls; R1 of 1.5 whorls, first half whorl practically smooth, gradually changing to widely, regularly-spaced, strong ribs (ca. 30 ribs on last half whorl of R1), present on entire R1 except area between peripheral keel and outer edge of periumbilical keel, which has fine spiral striation; some spiral striation visible on dorsum of R1, and between ribs; boundary between R1 and R2 distinct due to dense R2 ribs; R2 ribs curved toward aperture, ca. 34–36 R2 ribs present; spaces between R2 ribs narrower than ribs; R2+R3 more than quarter whorl (ca. 110˚); R2 considerably shorter than R3, slightly more half its length; boundary between R2 and R3 distinct due to change in sculpture and deep constriction; R3 with rounded, elongated swelling situated closer to constriction than to peristome; aperture strongly oblique to shell axis, rounded with basal incision; boundary between inner and outer peristomes not conspicuous; inner peristome strong, somewhat protruding, expanded, basal and palatal portions strongly fringed, outer peristome weaker, expanded, but reflected only in direction of umbilicus; umbilicus funnel-shaped, relatively narrow, less than one third of shell width.

Measurements. D: 2.9–3 mm, H: 1.9 mm

Operculum. Unknown.

Differential diagnosis. The angled body whorl, the funnel-shaped umbilicus, the flattened dorsal side, and the strongly convex R3 swelling distinguish this new species from the most similar D. fimbriatus ( Bavay & Dautzenberg, 1912) , which is known from Laos and Vietnam (Páll-Gergely et al. 2017). The R1 ribs of this species are stronger than those of most D. fimbriatus populations, and the new species has a spirally striated R1.

Dicharax sylheticus (Godwin-Austen, 1914) (Examined material: S. Sylhet Hills, W. Channel leg., NHMUK 1903.7.1.55, holotype, Fig. 16 ) is similar, but has a more elevated spire, a less keeled body whorl, a longer R2 with less dense ribs, and a rounded aperture.

Distribution. This new species is known only from the type locality ( Fig. 17 ).

Remarks. Similarly to some populations of D. omissus (Godwin-Austen, 1914) , this species also possesses spiral striation on R1, which is very rare in Dicharax . Spiral striation on the teleoconch is characteristic for Chamalycaeus , but this species is classified in Dicharax due to the curved R2 ribs characterizing that genus and its overall shell shape. Possible homology of the spiral striation of these few Dicharax species and other alycaeid genera needs further investigation.

Figures

FIGURE 14. Dicharax admirandus Páll-Gergely & Auffenberg, n. sp., holotype (UF 345861).

FIGURE 15. Sculpture of Dicharax admirandus Páll-Gergely & Auffenberg, n. sp., holotype (UF 345861).

FIGURE 16. Dicharax sylheticus (Godwin-Austen, 1914), holotype (NHMUK 1903.7.1.55).

FIGURE 17. Distribution of alycaeid species in northern Thailand and Myanmar. filled circle: Dicharax admirandus Páll- Gergely & Auffenberg, n. sp., empty square: Dicharax ebrius Páll-Gergely & Auffenberg, n. sp., filled triangle: Dicharax gnomus Páll-Gergely, n. sp., filled square: Dicharax mirounga Páll-Gergely, n. sp., inverted empty triangles: Dicharax verruco- sus Páll-Gergely & Hunyadi n. sp., rhombus: Dicharax stuparum Páll-Gergely & Hunyadi, 2018, empty triangle: Metalycaeus anas Páll-Gergely & A. Reischütz, n. sp.