Dicharax caudapiscis, Páll-Gergely & Hunyadi, 2018

Páll-Gergely, Barna & Hunyadi, András, 2018, Four new cyclophoroid species from Thailand and Laos (Gastropoda: Caenogastropoda: Alycaeidae, Diplommatinidae, Pupinidae), Zoosystema 40 (3), pp. 59-66 : 60-62

Dicharax caudapiscis n. sp.

( Fig. 1A-E )

TYPE MATERIAL. — Thailand. Chiang Rai Province, approx. 9 km south-southwest from Mae Sai, Wat Tham Pla , 400 m a.s.l., 20°19.723’N, 99°51.817’E, leg. Hunyadi A., 12.II.2015., HNHM 100177 (holotype, D = 1.92 mm, H = 0.98 mm) .

ETYMOLOGY. — The specific epithet caudapiscis (Latin: fish tail) refers to the name of the cave in the type locality (Wat Tham Pla = Fish Tail Cave).

TYPE LOCALITY. — Thailand, Chiang Rai Province, approx. 9 km southsouthwest from Mae Sai, Wat Tham Pla , 400 m a.s.l., 20°19.723’N, 99°51.817’E.

DIAGNOSIS. — A very small species with nearly flat shell, smooth R1, normally long R2 with dense, curved ribs, and a very short R3.

DIFFERENTIAL DIAGNOSIS. — The only such tiny alycaeid species in the neighbouring areas ( Myanmar, Thailand, adjacent Chinese provinces and Laos) are Dicharax (?) abdoui and Dicharax (?) ellipticus. Those species, however, possess a long, bluntly thickened R3, and lack curved ribs on the R2. Some tiny new Dicharax species are known from Peninsular Malaysia, but they all have a ribbed R2 and a longer R3. Dicharax caudapiscis n. sp. differs from D. stuparum n. sp. by the less oblique aperture, weaker R1 sculpture, and the much shorter R3.

DISTRIBUTION. — This species is known from the type locality only.

DESCRIPTION

Shell very small for the genus, off-white, nearly entirely flat, shell outline oval from standard dorsal view, body whorl rounded; protoconch with 1.5 whorls, glossy; R1 with c. 1.25 whorls, also glossy, with very fine, irregular growth lines (most prominent inside umbilicus); boundary between R1 and R2 clearly visible because R2 bears dense, curved ribs (c. 46 altogether); ribs curve posteriorly (= away from aperture) at proximal end of R2, whereas anteriorly (= towards aperture) at anterior end of R2; cross section of ribs and microtunnels could not be examined; R2 and R3 less than 90 degrees combined, R2 c. two times longer than R3; R2 and R3 separated by a shallow incision; R3 very short, without swelling; aperture rounded, only slightly oblique to shell axis; peristome thickened, reflected only in direction of umbilicus; inner peristome slightly protruding; boundary between inner and outer peristomes hardly visible. Operculum and soft anatomy unknown.

Measurements (in mm)

D = 1.92, H = 0.98.

REMARKS

Although Dicharax caudapiscis n. sp. and D. stuparum n. sp. are similar in terms of shell size, and the geographic distance between them is small, they are clearly distinct species because of the strikingly different proportions of shell regions.

Figures

FIG. 1. — Shells of Dicharax Kobelt & Möllendorff,1900 species:A-E, Dicharax caudapiscis n. sp.(holotype); F-K, Dicharax stuparum n. sp.(holotype).Photograph: Barna Páll-Gergely. Scale bars: A-C, F-H, 1 mm; D, 300 μm; E, K, 100 μm; I, J, 500 μm.