Pincerna viginticostatus, Páll-Gergely, 2023

Páll-Gergely, Barna, 2023, Revision of the Alycaeidae of China, Laos and Vietnam (Gastropoda: Cyclophoroidea) II: The genera Alycaeus and Pincerna, Zootaxa 5249 (2), pp. 253-276 : 272-274

Pincerna viginticostatus n. sp.

( Figs 14A–F )

Type material. Holotype (D= 4.2 mm, H=4.0 mm): VIETNAM, Lạng SƠn Province, B ắc SƠn District , Long Dong, 3.8 km from junction 1B- 241, 390 m a.s.l., 21°56.728′N, 106°19.447′E (locality code: 2020/51), leg. Hunyadi, A., 18 February 2020 ( HNHM 105383 , Figs 14A, B ) . Paratypes: Same data as for holotype, HA (2 shells).

Diagnosis. A medium sized Pincerna species with regularly ribbed R1, long R2 with ca. 20 slightly elevated ribs, R3 with blunt central swelling, clearly separate inner and outer peristomes, a protruding inner peristome, and a closed umbilicus.

Description. Shell yellowish-corneous or off-white, although all three available shells were somewhat corroded; slightly wider than high; protoconch smooth, yellowish, consisting of ca. 1.5–1.75 whorls; R1 of ca. 1.5 whorls, with widely-spaced, thread-like, regular ribs (strongest near the suture) and extremely fine spiral striation; ribs ca. 26–28 on last half whorl of R1; R2 and R3 approx. 110 degrees combines, R2 ca. half of length of R3; constriction between R2 and R3 relatively shallow; R2 with ca. 20–22 regular, slightly elevated, dense ribs; cross-sectional view not examined; R3 with long, central swelling, with 3–4 thread-like ribs on its anterior part; aperture rounded; outer peristome expanded and reflected at the basal and columellar part; inner peristome protruding, expanded; boundary between inner and outer peristomes clearly visible; umbilicus entirely closed by reflected outer peristome.

Operculum. Unknown.

Differential diagnosis. This new species is similar to P. vanbuensis in shell shape, but differs from it in the R2 sculpture. While in P. vanbuensis the R2 is smooth and consists of 46–60 lighter and darker alternating stripes, this new species has ca. 20–22 slightly elevated ribs. Pincerna maolanensis (which is possibly a synonym of P. vanbuensis ) also possesses a smooth R2.

Measurements (in mm). D = 4.1–4.2, H = 3.9–4.0 (n = 3).

Etymology. The specific epithet (meaning twenty ribs) refers to the key character of this species (presence of ca. 20 R2 ribs instead more numerous lighter and darker alternating stripes of P. vanbuensis ).

Distribution. This new species is known only from the type locality ( Fig. 13 ).

Remarks. This species differs from Pincerna vanbuensis only in the fine morphology of R2 sculpture. This is not unusual in the family Alycaeidae . For example, Dicharax moellendorffi (Kobelt & Möllendorff, 1886) differs from the otherwise very similar Dicharax cristatus ( Möllendorff, 1886) by the smooth R2 (Páll-Gergely et al. 2017). Also, Metalycaeus minatoi Páll-Gergely, 2017 possesses a smooth R2, while that of M. vinctus ( Pilsbry, 1902) , which is its putative sister species, is ribbed ( Páll-Gergely & Asami 2017).

Figures

FIGURE 13. Distribution of Pincerna Preston, 1907 species. Circles: Pincerna vanbuensis (Bavay & Dautzenberg, 1900); White rhomb: Pincerna maolanensis (Luo, Zhang & Zhuo, 2009); Green triangle: Pincerna viginticostatus n. sp. Yellow circle: samples examined in this study; Red circles: Samples mentioned by Do & Nguyen 2022; White circle: type locality of Pincerna clausus Do & Nguyen, 2022 (synonym of P. vanbuensis). The map was made using Google Earth Pro.

FIGURE 14. Shells of Pincerna Preston, 1907 species.A–F: Pincerna viginticostatus n. sp. (holotype, HNHM 105383); G: R2 of Pincerna vanbuensis (Bavay & Dautzenberg, 1900) (MNHN-IM-2012-27215, same as on Fig. 12E). All photos: B. Páll-Gergely.