Hypselostoma torta Gojšina, Auffenberg & Páll-Gergely, 2025

Hypselostoma torta Gojšina, Auffenberg & Páll-Gergely sp. nov.

Type material.

Holotype. Thailand • 1 shell (SH: 3.8 mm, SW: 3.5 mm); Nakhon Sawan Province 19.5 m NE intersection Hwys 11 and 32 ; 15°14'N, 100°16'E; 50 m a. s. l.; 02. May 1988; K. Auffenberg leg.; locality code KA-0696 ; UF 591362 GoogleMaps . Paratypes. Thailand • 2 shells; same data as for holotype; CUMZ 14462 View Materials GoogleMaps • 20 shells; same data as for holotype; UF 346125 GoogleMaps • 18 shells; same data as for holotype; locality code KA-0697 ; UF 346133 GoogleMaps • 4 ethanol-preserved shells; same data as for holotype; locality code KA-0696 ; UF 591361 GoogleMaps .

Additional material examined.

Thailand • 5 shells (juveniles, not paratypes); same data as for holotype; locality code KA-0697 ; UF 583727 GoogleMaps .

Type locality.

Thailand, Nakhon Sawan Province 19.5 m NE intersection Hwys 11 and 32; 15°14'N, 100°16'E; 50 m a. s. l.

Diagnosis.

A Hypselostoma with all teleoconch whorls shouldered and very weakly spirally striated. Spiral striae not raised. Last whorl detached from the penultimate and slightly descending. Four weak barriers in the aperture. Columellar lamella is like a strong swelling, forming a basal furrow.

Description.

Shell concave-conical (due to the strongly enlarged last whorl), brownish, consisting of 5–5.5 whorls separated by a very deep suture. Protoconch finely pitted, not showing spiralling pattern, rounded, same colour as the initial teleoconch whorls but slightly lighter than the last whorl. First two teleoconch whorls weakly shouldered, penultimate strongly and the last whorl is very strongly shouldered. The outline of the last and the penultimate whorl above the shoulder is concave (forming a flat platform). This surface is on initial teleoconch whorls more sloping. Whole teleoconch surface is weakly spirally striated (these spiral striae are not thread-like raised as in many congeners, but very blunt and indistinct) and occasionally crossed by radial growth lines and several thicker, whitish radial streaks which are rather unevenly positioned. These whitish streaks seem to be the densest on the penultimate whorl. Last whorl convex at its base, towards the umbilicus. It is slightly to moderately detached from the penultimate whorl and slightly descending near the aperture (~ 15–25 ° compared to the shell axis). Peristome very strong, dirty white, expanded but not reflected. Aperture equipped with three or four barriers (parietal (angulo-parietal?), upper palatal, lower palatal (sometimes absent), and columellar). There are no smaller barriers between the main ones. Parietal lamella is strong, high, and triangular when observed in perpendicular view. There is a very small tubercle-like swelling in front of the parietal lamella which may be homologous with the angular part of the usually present angulo-parietal (or just angular) in other congeners. Upper palatal plica moderately strong, almost twice as weak as the parietal lamella. Lower palatal plica very weak and low, dot-like, sometimes absent. Columellar lamella not present in its usual form (its borders are not clearly delimited) but as a rather strong, swelled part of the aperture which forms a prominent basal furrow below it (similar to the one present in H. fungus sp. nov.). The shape of the columellar side of the aperture is also reminiscent of the playground slide. Surface of all apertural barriers is smooth. Sinulus wide, distinctly separated from the rest of the aperture. Umbilicus wide, measuring ~ 1 / 3 of the shell width, expanding at the last whorl. Inside the umbilicus, there is a strong groove present, stretching across the whole last whorl.

Differential diagnosis.

This species is not similar to any of its congeners. It most closely resembles some Aulacospira species (e. g., A. pluangtong , A. smaesarnensis ). However, it has a much wider umbilicus than both species as well as spiral striation and way more strongly shouldered whorls.

Measurements

(in mm, n = 5). SH = 3.45–3.8; SW = 2.83–3.62; AH = 1.62–1.82; AW = 1.38–1.84.

Etymology.

Since all whorls of this species are shouldered, the shell has an appearance of the wedding cake. The specific epithet torta comes from a Serbian word torta meaning a cake. To be used as a noun in apposition.

Distribution.

This species is known only from the type locality.

Remarks.

The shell of this species can sometimes be more depressed so that it is almost as wide as high. This species may belong to a separate genus or it may be closely related to some Aulacospira species ( A. pluangtong , A. smaesarnensis ). However, due to the different shell shape (concave-conical), height (> 3.4 mm) and surface sculpture (delicate, non-raised spiral striae) from typical Aulacospira species (inhabiting the Philippines), we provisionally place this species in the genus Hypselostoma .