Sinoennea bounphanmyae Inkhavilay and Vanhdibay sp. n.

(Figures 1 (b), 2, 4(b))

http://www.zoobank.org/urn:lsid:zoobank.org:act:81AE2C7F-3C60-405E-9BD5-

265D068C9D19

Type material

Holotype CUMZ 14207 (height 4.0 mm, width 2.3 mm, 6½ whorls; Figures 2 (a) and 4(b). Paratypes CUMZ 14208 (3 shells; Figure 2 (b, c) and NHMUK (1 shell) all have the same collecting data as the holotype.

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Type locality

The limestone outcrop at Pha Thor Nor Kham Hills, Feuang District, Vientiane Province, Laos (18.702556°N, 102.131778°E).

Etymology

The species is dedicated to Professor Dr Somchanh Bounphanmy, Vice President of the National University of Laos, to acknowledge her great support for biodiversity research in Laos, which has resulted in the discovery of this new species, and for her part in initiating collaborative research on biodiversity. Moreover, it is dedicated in regard to her support of many young Laotian taxonomists.

Diagnosis

Ovate, nearly smooth surface, and glossy shell; ear-shaped aperture; apertural dentition with five folds (parietal, two palatal, and two columellar); umbilicus wide and with periumbilical groove.

Description (Figure 2)

Shell ovate, opaque to semi-translucent, and glass-like. Shell height 3.6–4.2 mm, shell width 2.3–2.5 mm, and with 5–6½ whorls. Protoconch around two whorls, smooth and glossy with very fine growth lines and traces of inconspicuous wrinkles at suture. Teleoconch glossy, generally smooth to thin growth lines, strong and regularly ribbed, are occasionally present near varix (probably juvenile peristomes), behind expanded lip, and below periphery surrounding umbilicus. When present, individual ribs are strong, curved and regularly spaced. Whorls blunt to slightly bulging; suture wide and impressed. Aperture ear-shaped with stronger depression on palatal wall than on columella wall; peristome thickened, expanded, and slightly reflected. Parietal callus thickened, elevated, and does not reach half of preceding whorl. Apertural dentition with five folds. Parietal lamella (p) very strong and elevated: outer portion slightly curved, oblique, bent in direction of columella; inner part lower and bent. Sinulus relatively wide, elongated, and opens laterally. Upper palatal plica (upl) thickened, slightly smaller than palatal plica, and situated on lip; lower palatal plica (lpl) thickened, strong, and situated slightly inside aperture. Columellar (c) and subcolumellar (sbc) lamellae comparable in size, strong, thick, and situated some distance from peristome; subcolumellar lamella located further inside aperture rather than columellar lamella. Umbilicus widely opened, rounded, deep, surrounded by prominent periumbilical keel; inner part of last whorl with periumbilical groove to peristome.

Distribution

Currently, this new species is only known from its type locality (Figure 1 (a)). This limestone-rich karst lies beside the Nam Lik River in the Feuang District, Vientiane Province. The area is covered with primary forests at its margins and is still relatively well vegetated with a low level of disturbance.

The snails were found crawling among the decaying leaf litter under a rock overhang at the base of a limestone hill in a humid and moist environment. The living snails were pale and monochrome yellowish; the upper tentacles were elongated, cylindrical, and stout with dark eyespots on the tip, while the lower tentacles were very short (Figure 1 (b)).

Differential diagnosis

Sinoennea bounphanmyae sp. n. differs from S. infantilis Páll-Gergely and Grego in Páll-Gergely, Reischütz et al. 2020 and S. variabilis Páll-Gergely and Grego in Páll-Gergely et al. 2020, in that it has a much larger (height> 3.6 mm; Table 1) and ovate shell, and an ear-shaped aperture. In contrast, the latter two species (Figure 4 (g,h)) have relatively smaller (height <2 mm; Table 1) and cylindrical shells with triangular apertures (Páll-Gergely, Reischütz et al. 2020).

In comparison with superficially similar Laotian species, S. bounphanmyae sp. n. can be distinguished from S. otostoma Páll-Gergely, Reischütz and Maassen in Páll-Gergely et al. 2020b and S. ljudmilena Páll-Gergely in Páll-Gergely, Reischütz et al. 2020 by rarely having radial ridges, having two palatal plicae, two columellar lamellae, and a wide umbilicus (with periumbilical groove), and not having a swelling on the inner part of the last whorl. In comparison, S. otostoma (Figure 4 (f)) and S. ljudmilena (Figure 4 (i)) possess smooth shells, one large columellar lamella, a narrow umbilicus (without a periumbilical groove), and swelling on the inner part of the last whorl. Additionally, S. otostoma has a convex whorl and deeper sutures, whereas S. ljudmilena has a strongly ribbed suture and three palatal plicae (Páll-Gergely, Reischütz et al. 2020).

This new species also differs from S. angustistoma Páll-Gergely, Reischütz and Maassen in Páll-Gergely, Reischütz et al. 2020 in having a smooth shell (rarely with radial ridges), an ear-shaped aperture, a shallower suture, two palatal plicae, and two columellar lamellae. In contrast, S. angustistoma (Figure 4 (a)) possesses an evenly-ribbed entire shell, an elongated ovate aperture, a deeper suture, three palatal plicae, and three columellar lamellae (Páll-Gergely, Hunyadi et al. 2020).

Sinoennea bounphanmyae sp. n. can be differentiated from the Thai species S. loeiensis Tanmuangpak and Tumpeesuwan in Tanmuangpak et al. 2015 by rarely having radial ridges with a very weak rib at the suture, having an ear-shaped aperture, two separated palatal plicae, and two columellar lamellae. In comparison, S. loeiensis (Figure 4 (k)) possesses a generally smooth shell with a strongly ribbed suture, an ovate aperture, connected upper and lower palatal plicae (bifid), one basal plica, and one large columellar lamella (Tanmuangpak et al. 2015).

This new species can also be distinguished from S. calva (Dautzenberg, 1894) from Vietnam by having generally smooth shells, ear-shaped aperture, and two columellar lamellae, while S. calva (Figure 4 (j)) has a solid ribbed shell and an ovate aperture.

Additionally, S. bounphanmyae sp. n. can be differentiated from the Parasinoennea Chen and Páll-Gergely in Páll-Gergely, Hunyadi et al. 2020 species from Vietnam, P. demangei (Bavay and Dautzenberg, 1912), P. formica (Bavay and Dautzenberg, 1912), and P. ovulum (Bavay and Dautzenberg, 1912), by having generally smooth shells, ear-shaped apertures, elevated parietal callus, and two columellar lamellae. In comparison, these three species possess triangular aperture, parietal callus adnate to the last whorl, some degree of swelling on the inner part of the last whorl near the peristome, and one large columellar lamella inside the aperture. Moreover, P. demangei (Figure 4 (o)) has a ribbed shell and a weak basal plica, P. formica (Figure 4 (p)) has a solid rib at the suture, and P. ovulum (Figure 4 (q)) has an ovate aperture, is strongly ribbed at the suture, and has a weak basal plica (Dautzenberg 1894; Bavay and Dautzenberg 1912).

Remarks

Although the type locality of S. bounphanmyae sp. n. is close to those of S. otostoma and S. loeiensis (approximately 40 and 120 km apart, respectively), the three species clearly have distinct shell morphologies. This endemism of karst-restricted taxa is possibly caused by the low dispersal ability of the snail itself and the fragmented and isolated characteristics of the limestone, which then serves as habitat islands (Sutcharit et al. 2020).