Hypselostoma sorormajor Gojšina, Hunyadi & Páll-Gergely, 2025

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

Type material.

Holotype. Cambodia • 1 shell (SH: 2.70 mm; SW 1: 3.91 mm); Steung Treng Province, 55.7 km northwest + 2 km north from Stung Treng Mekong Bridge, Chap Phleung Mt. ( Neak Khiev Mt. ); 13°47.821'N, 105°36.205'E; 135 m a. s. l.; 26 Oct. 2023, A. Hunyadi & J. U. Otani leg.; CUMZ 14459 View Materials GoogleMaps . Paratypes. Cambodia • 28 shells; same data as for holotype; coll. HA GoogleMaps .

Additional material examined.

Cambodia • 3 shells (2 damaged and 1 juvenile, not paratypes); same data as for holotype; coll. HA GoogleMaps • 41 shells; Steung Treng Province, 40 km northwest + 2 km north from Stung Treng Mekong Bridge , limestone mountain at the left side of the joining road; 13°45.568'N, 105°43.644'E; 135 m a. s. l.; 26 Oct. 2023; A. Hunyadi & J. U. Otani leg.; coll. HA GoogleMaps • 78 shells; Steung Treng Province, Stung Treng Mekong Bridge , 45 km NWN + 400 m N, limestone hill, right side of the road # 64; 13°45.866'N, 105°41.154'E; 180 m a. s. l.; 26 Oct. 2023; A. Hunyadi & J. U. Otani leg.; coll. HA GoogleMaps • 1 shell; same data as previous; coll. VG GoogleMaps • 26 shells; Steung Treng Province, 36.3 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.; coll. HA GoogleMaps .

Type locality.

Cambodia, Steung Treng Province, 55.7 km northwest + 2 km north from Stung Treng Mekong Bridge, Chap Phleung Mt. (Neak Khiev Mt.); 13°47.821'N, 105°36.205'E; 135 m a. s. l.

Diagnosis.

A Hypselostoma species with depressed, concave-conical shell, bluntly and strongly keeled last whorl, raised spiral striation, hooked apertural barriers (upper palatal, interpalatal, lower palatal and basal) and very wide umbilicus. Angular and parietal lamellae fused. Shell width reaches 4 mm.

Description.

Shell depressed, concave-conical, brown to yellowish-brown, consisting of 4.75–5.5 whorls separated by a deep suture. Protoconch slightly lighter than the rest of the shell, finely pitted, showing spiralling pattern initially and clearer spiral striae terminally. It is 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 or rarely shallow groove. All whorls densely sculptured with strong, raised spiral striae crossed by less dense radial growth lines and occasionally by a few thick, whitish radial streaks. Spacing between the spiral striae irregular, but usually around the width of two to four spiral striae. Last whorl moderately detached from the penultimate and moderately ascending (~ 35 ° compared to the shell axis). Peristome expanded, not reflected, its surface finely pitted. Aperture equipped with four 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 the 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. Sometimes, there is a deep constriction between the angular and parietal part so that these lamellae appear almost separated (as in former Gyliotrachela ). Upper and lower palatal plicae are hooked, pointing outside and roughly the same size. Columellar lamella thick and almost horizontal. Of smaller barriers, there is usually one hooked interpalatal, one infrapalatal, one basal plica (hooked or blunt) and one blunt lamella in the columello-parietal transition embayment. Of them, the strongest one is the basal, which is almost as strong as the palatals. A distinct swelling is also observed at the palatal side (in front of the upper palatal and interpalatal plicae) which is probably homologous to the palatal tubercle in the majority of Bensonella species. Surface of all apertural barriers is finely granulated. Sinulus rounded, distinctly separated from the rest of the aperture. Umbilicus very wide, measuring ~ 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 hooked apertural barriers. Hypselostoma aquila sp. nov. is much smaller, more slender and has a narrower umbilicus. For differences from H. sororminor sp. nov. see under that species.

Measurements

(in mm, n = 15). SH = 1.62–2.78; SW 1 = 2.44–4.01; SW 2 = 1.57–2.56; AH = 0.85–1.71; AW = 0.81–1.46.

Etymology.

The name of this species is derived from two Latin words, soror meaning sister and major meaning greater, larger, or elder, which serves as a comparison with similar but smaller H. sororminor sp. nov.

Distribution.

This species is known from four closely situated localities in Steung Treng Province.

Remarks.

This is a very variable species in terms of shell size. These different “ forms ” were not regarded as distinct species since there were no other significant morphological differences noticed. The angulo-parietal lamellae were sometimes clearly fused, while sometimes almost completely separated. 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. sorormajor sp. nov., it is possible that this species can be found here as well and be threatened by quarrying.