Hypselostoma sororminor Gojšina, Hunyadi & Páll-Gergely, 2025

Hypselostoma sororminor Gojšina, Hunyadi & Páll-Gergely sp. nov.

Type material.

Holotype. Cambodia • 1 shell (SH: 2.44 mm; SW 1: 3.57 mm); Steung Treng Province, 36.6 km northwest + 3.1 km north from Stung Treng Mekong Bridge , limestone mountain on the left side of the joining road; 13°45.585'N, 105°44.930'E; 130 m a. s. l.; 25 Oct. 2023, A. Hunyadi & J. U. Otani leg.; CUMZ 14460 View Materials GoogleMaps . Paratypes. Cambodia • 32 shells; same data as for holotype; coll. HA GoogleMaps • 1 shell; same data as for holotype; coll. VG GoogleMaps .

Additional material examined.

Cambodia • 2 shells (juveniles / damaged, not paratypes); same data as for holotype; coll. HA GoogleMaps .

Type locality.

Cambodia, Steung Treng Province, 36.6 km northwest + 3.1 km north from Stung Treng Mekong Bridge, limestone mountain on the left side of the joining road; 13°45.585'N, 105°44.930'E; 130 m a. s. l.

Diagnosis.

A Hypselostoma species with depressed, concave-conical shell, bluntly and strongly keeled last whorl, raised spiral striation, blunt apertural barriers (altogether 6 or 7) and very wide umbilicus. Angular and parietal lamellae fused.

Description.

Shell depressed, concave-conical, brown, consisting of 5–5.5 whorls separated by a deep suture. Protoconch lighter than the rest of the shell, coarsely spirally striated (~ 12 striae) and consisting of 1.25–1.5 whorls. Protoconch and initial teleoconch whorls rounded, penultimate weakly convex. Last whorl with strong but blunt keel positioned at the centre of the periphery. Above the keel there is a deep groove. All whorls densely sculptured with strong, raised spiral striae crossed by less dense radial growth lines and occasionally by a few thin, whitish radial streaks. Spacing between the spiral striae irregular, but usually around the width of two, three, or four spiral striae. Last whorl slightly to moderately detached from the penultimate and slightly to moderately ascending near the aperture (~ 25–35 ° compared to the shell axis). Peristome expanded, not reflected, its surface finely pitted. Aperture equipped with four strong, main barriers (angulo-parietal, upper palatal, lower palatal, and columellar) and several smaller ones. Angulo-parietal lamella strong, its angular part is leaned towards the palatal side while its parietal part is leaned towards the columellar side. Angular part is pointed and smaller than the parietal. It is the only barrier reaching the expanding peristome. Upper and lower palatal plicae approximately the same size, the lower palatal being longer and more slender. Upper palatal plica slightly bent towards the lower palatal. Columellar lamella very thick and almost horizontal. Of smaller barriers, a small and weak interpalatal plica is present, stronger (but still weak) basal and a moderate knob-like plica in the columello-parietal transition embayment. A weak swelling is also observed at the palatal side (in front of the upper palatal plicae) which is probably homologous to the palatal tubercle in the majority of Bensonella species. Surface of all apertural barriers is densely granulated. Sinulus rounded, distinctly separated from the rest of the aperture. Umbilicus very wide, measuring between 1 / 3 and ½ of the shell width. There is a periumbilical keel situated on the last ~ 0.75 whorl right above the umbilicus. Along this keel there is a deep groove on the umbilical side.

Differential diagnosis.

This species differs from H. discobasis in the less slender shell and less numerous apertural barriers which are also thicker. It differs from H. sorormajor sp. nov. in its smaller dimensions and apertural barrier arrangement: it has less numerous barriers, none of which are hooked (in contrast to H. sorormajor sp. nov.). Hypselostoma aquila sp. nov. is smaller, more slender, has a narrower umbilicus and hooked barriers.

Measurements

(in mm, n = 5). SH = 2.37–2.57; SW 1 = 3.20–3.61; SW 2 = 2.05–2.40; AH = 1.25–1.42; AW = 1.22–1.26.

Etymology.

The name of this species is derived from two Latin words, soror meaning sister and minor meaning smaller which serves as a comparison with similar but usually larger H. sorormajor sp. nov.

Distribution.

This species is only known from the type locality.

Remarks.

The largest, and still unexplored limestone hill in Steung Treng Province (13°47.941'N, 105°43.7671'E) was inaccessible during the collecting efforts in 2023 due to the works of a cement factory. Due to the proximity of this hill to the type locality of H. sororminor sp. nov., it is possible that this species can be found here as well and be threatened by quarrying.