Pincerna clausa, Sang & Son, 2022

Sang, Do Duc & Son, Nguyen Thanh, 2022, The land snail genus Pincerna Preston, 1907 (Gastropoda: Alycaeidae) from Vietnam and Laos, with description of a new species, Raffles Bulletin of Zoology 70, pp. 364-375 : 372-373

Pincerna clausa , new species

( Figs. 1 , 4A–C , 5A–F , 6D ; Tables 1, 2)

Type material. Holotype (1 shell, height 5.2 mm, width 5.0 mm; Figs. 4A , 6D ) ( VNMN-IZ 002.304 ), Vietnam, Điện Biên Province , Điện Biên District, Na Ư Commune, near Tây Trang international border gate at the Vietnam - Laos border region, exposed limestone with little soil and vegetation of herbs, 814 m a.s.l., 21°13′34″N, 102°58′3″E, col. D.S. Do & C. Vilachark, 08 December 2018 ; Paratypes: 3 paratypes ( ZMHU. MOL 044 ), same data as holotype .

Etymology. This new species is named for its conspicuous closed umbilicus (Latin: clausa = close).

Diagnosis. Pincerna clausa , new species, is characterised by a small sized, globular shell with clearly spiral striation on R1 and a closed umbilicus, which is completely obscured by the reflected columellar extension.

Description. Shell globose, off-white, rather glossy, medium sized (height 5.1–5.3 mm, width 4.9–5.0 mm). Spire high, slightly obtuse (spire height 1.3–1.4, spire width 1.8–2.0 mm). Whorls 4.25–4.5, the periphery rounded. Suture rather deep. Protoconch smooth, glossy, without spiral striation, 1.25–1.75 whorls. R1 of 2.0 whorls, with rather regular, indistinct and low ribs, and clearly spiral striation; on the first part of R1 the ribs are rather weak and irregular, on the last part, however, they are close together and sharp, with well visible spiral striation ( Figs. 4 , 6D ). R1 and R2 boundary conspicuous due to denser and slender R2 ribs. R2 and breathing tube relatively long (breathing tube length ca 1.2–1.4 mm), consisting of 34–41 stripes, which are slender and slightly elevated from the surface, overall surface slightly wrinkled. R3 slightly longer than R2; boundary between R2 and R3 distinct due to constriction and change in sculpture. R3 smooth, glossy, with some widely spaced, irregular and weak ribs on the terminal part. Aperture circular, moderately expanded (aperture diameter 3.0–3.1 mm). Peristome double, slightly thickened; outer peristome sharp, expanded but not reflected; inner peristome protruding, sharp; outer and inner peristomes are clearly separated. Umbilicus narrow and completely obscured by the reflected columellar extension.

Operculum. Unknown.

Distribution. The new species is thus far known only from the limestone hill in Na Ư Commune, Điện Biên District, Điện Biên Province, northwest Vietnam ( Fig. 1 ).

Remarks. This new species has a similar shell shape as Pincerna vanbuensis but differs in having a closed umbilicus, stronger spiral striation on R1, and weaker ribs on R2. Pincerna clausa , new species, also resembles Pincerna costulusus in shell shape but differs in its more pronounced spiral striation as well as R1 with denser and weaker ribs. It differs from Pincerna anceyi by having much stronger, more widely-spaced ribs, well visible spiral striation and closed umbilicus. It differs from P. mouhoti by having a narrow umbilicus and smaller shell size.

Figures

Fig. 1. Distribution of Pincerna species in Vietnam and Laos. Triangle: Pincerna anceyi; Grey circle: Pincerna costulosus; Black circles: Pincerna mouhoti; Squares: Pincerna vanbuensis; Star: Pincerna clausa, new species. The localities are detailed in Table 1.

Fig. 4. Shell (apertural view, dorsal view, ventral view, and side view) of Pincerna clausa, new species. A, holotype VNMN-IZ 002.304; B, C, paratypes ZMHU. MOL 044.

Fig. 5. Details of the shell of Pincerna clausa n. sp. (holotype VNMN-IZ 002.304). A–B, protoconch; C, R2 and sutural tube; D, R3 and boundary between R2 and R3; E, aperture; F, umbilicus.

Fig. 6. Synoptic view of Vietnamese and Laos Pincerna species. A, MNHN-IM-2000-31797; B, NHMUK 20170120; C, MNHN- IM-2000-31786; D, VNMN-IZ 002.304; E, MNHN-IM-2000-31798.