The land snail genus Pincerna Preston, 1907 (Gastropoda: Alycaeidae) from Vietnam and Laos, with description of a new species Author Sang, Do Duc Author Son, Nguyen Thanh text Raffles Bulletin of Zoology 2022 2022-06-01 70 364 375 journal article 10.26107/RBZ-2022-0018 2345-7600 7174164 E3A5AA23-BEAE-445E-981F-93A9E7A79417 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. Table 1. Shell size variation of Pincerna spp. specimen collections in this study

Species and locality	No. of specimens	Shell height (SH, in mm)	Shell width (SW, in mm)	SH/SW ratio	Aperture diameter (in mm)
Pincerna anceyi
1. Tonkin, Vietnam ( Mabille, 1887 )	–	5.0	3.5–5.0	1.00	–
Pincerna costulosus
2. Khổng Lào, Phong Thổ, Lai Châu, Vietnam	4	4.8–5.3	4.6–5.2	1.02–1.04	2.4–2.8
Pincerna mouhoti
3. Ngoy, Luang Phrabang, Laos ( Inkhavilay et al., 2019 )	–	5.25	6.3–7.7	0.68	–
4. Hang Kia – Pà Cò Nature Reserve, Hòa Bình, Vietnam	7	6.2–6.5	6.5–6.9	0.92–0.97	3.5–3.8
5. Pa Cốp, Vân Hồ, SƠn La, Vietnam	10	6.2–6.5	6.2–7.0	0.94–1.00	3.4–3.8
6. Thẳm Bó Cave, MƯờng La, SƠn La, Vietnam	17	6.8–7.1	6.7–6.8	1.00–1.04	3.8–4.0
7. Lằn, MƯờng Do, Phù Yên, SƠn La, Vietnam	2	6.9–7.0	6.7–6.8	1.02–1.03	3.7–3.8
8. Copia Nature Reserve, SƠn La, Vietnam	3	6.0–6.2	6.2–6.3	0.95–1.00	3.2–3.4
Pincerna vanbuensis
9. Copia Nature Reserve, SƠn La, Vietnam	20	5.4–5.6	5.7–5.8	0.93–0.97	3.1–3.3
10. Chi Đảy Cave, Yên Châu, SƠn La, Vietnam	5	4.5–4.8	5.0–5.2	0.90–0.93	2.5–2.7
11. Tân SƠn, Mai Châu, Hòa Bình, Vietnam	4	4.9–5.0	5.0–5.1	0.90–0.94	2.5–2.6
12. Cúc PhƯƠng N.P., Ninh Bình, Vietnam	9	4.8–5.1	4.9–5.0	0.96–1.02	2.4–2.6
13. Nam Phan, Khoune, Xieng Khaong, Laos	26	5.0–5.4	5.3–5.7	0.93–0.95	2.8–3.0
14. Xiengkho, Houaphanh, Laos	18	5.0–5.1	4.9–5.2	0.95–1.04	2.8–3.1
Pincerna clausa , new species
15. Na Ư, Điện Biên, Điện Biên, Vietnam	4	5.1–5.3	4.9–5.0	1.04–1.06	3.0–3.1

Table 2. Comparison of diagnostic conchological characters among Pincerna species in this study.

Species	Sculpture of R1	No. of R2 ribs	R2 length compared to R3	Umbilicus	Number of whorls
P. anceyi	weakly ribbed	26	≤ R3	narrow	4.5
P. costulosus	strongly ribbed	14–20	≤ R3	narrow	4.5–5.0
P. mouhoti	strongly ribbed	35–76	≥ R3	wide	4.5
P. vanbuensis	strongly ribbed	65–71	~ R3	narrow	4.25–4.5
P. clausa	weakly ribbed	34–41	≤ R3	closed	4.25–4.5

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.