Alycaeus himalayae, Aravind & Páll-Gergely, 2023

Aravind, Neelavar Ananthram & Páll-Gergely, Barna, 2023, Two Extraordinary Alycaeid Species From Northeastern India (Gastropoda: Caenogastropoda: Cyclophoroidea), Acta Zoologica Academiae Scientiarum Hungaricae 69 (4), pp. 353-363 : 357-359

Alycaeus himalayae sp. n.

http://zoobank.org/ B31A16F4-C4AB-4B0A-AFB7-3611293CFDCC ( Figs 2–3 )

Material examined: India, Arunachal Pradesh, East Siang District, Yemsing , 28.136632°N, 95.012876°E, 514 m a.s.l., leg. N.A. Aravind & Surya Narayanan, 27 April 2022 (holotype ZSI/ SRC LM 1045 + paratype in ethanol ZSI/ SRC LM 1046 ). Holotype measurements: D: 7.4 mm, H: 6.1 mm.

Diagnosis: An Alycaeus species with light yellow colour, and a trumpet-like calcareous projection on the outer side of the operculum.

Description: Shell shape slightly concave conical, apex acute, colour light yellowish; whorls 5.25, rather regularly increasing with the exception of the last whorl, which domi- nates the appearance of the shell with its width; protoconch consisting of ca. 2 whorls, elevated, high-spire, finely granular (fig. 3D); R2 of ca. 2.75 whorls, its first ca. half whorl rather granular, but fine, irregular ribbing and even finer spiral striation also discernible; rib density increases towards end of R1, but on the last ca. 0.5–1 R1 whorl spiral striation nearly disappears; R2 inflated, with ca. 50 ribs; R2 ribs higher than R1 ones, and more conspicuous due to white breathing tunnels ( Fig. 3C ); R2+R3 approximately half whorl together, of com- parable length, and are separated by a shallow constriction; R3 with a long central swelling; R3 sculpture is characterized by irregular, mostly fine radial growth lines (although there are some stronger ribs in the middle), no spiral striation visible; aperture strongly oblique to shell axis, peristome strongly expanded, boundary between inner and outer peristomes clearly visible under microscope ( Fig. 3A ); inner peristome not protruding, it is smeared onto reflected outer peristome; umbilicus rounded, relatively narrow, shows all whorls.

Measurements: H = 7.3–7.4 mm, D = 6.1 mm.

Operculum: Outer surface glossy, with an elevated, trumpet-like calcareous elevation in the middle. It is clearly visible that this trumpet-like projection is a result of the rolling of an elevated lamina, because the overlapping edges of the lamina are visible, and at their meeting point the trumpet is lower ( Fig. 3B ).

Differential diagnosis: This new species differs from all other Himalayan alycaeid species by the yellowish, conical shell. The most similar shell in the vicinity is Stomacosmethis spratti ( Godwin-Austen, 1888) from Shan States, Myanmar, but it has a short sutural tube. Alycaeus himalayae sp. n. differs from all other Alycaeus species by the characteristic trumpet-like projection on the outer side of the operculum. Additional comparisons with other Alycaeus species are not necessary because each Alycaeus species have its own characteristic features that would distinguish it from this new species.

Etymology: The specific epithet himalayae refers to the Himalayan distribution of this species, which is a surprise as all other known Alycaeus so far reported from southeast Asia.

Distribution and ecology: This new species is known only from the type locality ( Fig. 4 ). Alycaeus himalayae sp. n. was collected from the entrance of a small limestone cave next to the road from Yemsing to Pangi. The snails were found in the wet cave wall amongst mosses and dripping water. Along with Alycaeus himalayae sp. n., other alycaeids and ariophantids were found. The surrounding vegetation is an evergreen forest with a thick canopy cover.

Remarks: The characteristic calcareous trumpet-like projection on the operculum seems to be unique for this species, but similar elevated struc- tures are known in the Alycaeidae . For example, Stomacosmethis kuekenthali (P. Sarasin et F. Sarasin, 1899) from Sulawesi and S. porcilliferus ( Bollinger, 1918) from eastern Borneo have elevated, trumpet-like projections, but in those two species the edge of the trumpet is thickened and reflected, and they are seem- ingly not made of a single rolled lamina, while the edge of the trumpet is sharp and not reflected in the new species, and it is made of a single rolled lamina. Furthermore, Dicharax bison Páll-Gergely et Hunyadi, 2017 (described in PÁLL-GERGELY et al. 2017) also has an elevated funnel-shaped projection on the outer side of the operculum, but it is clearly made of the multispiral outer lamina. It seems that the morphologically somewhat similar trumpet- or funnel-shaped projections on the outer side of the operculum of various alycaeid species are not homologous with each other, and probably developed multi- ple times during the evolution of this family.

Figures

Fig. 2. Holotype of Alycaeus himalayae sp. n. (Photos: B. Páll-Gergely)

Fig. 3. Operculum (A, B), sculpture of R2 (C) and protoconch (D) of the holotype of Alycaeus himalayae sp. n. (Photos: B. Páll-Gergely)

Fig. 4. Distribution of the genus Alycaeus Gray, 1850 (based on PÁLL-GERGELY et al. 2020 and PÁLL-GERGELY 2023). Dark grey area: Alycaeus s. str., Light grey area: distribution of Pincerna mouhoti (L. Pfeiffer, 1862) and Pincerna vanbuensis (Bavay et Dautzenberg, 1900),