Hypselostoma platybasis Gojšina, Hunyadi & Páll-Gergely, 2025

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

Type material.

Holotype. Cambodia • 1 shell (SH: 2.60 mm; SW: 2.56 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 14457 View Materials GoogleMaps . Paratypes. Cambodia • 160 shells; same data as for holotype; coll. HA GoogleMaps • 1 shell; same data as for holotype; coll. VG GoogleMaps .

Additional material examined.

Cambodia • 10 shells (juveniles, not paratypes); same data as holotype; coll. HA GoogleMaps .

Type locality.

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.

Hypselostoma species with bluntly keeled penultimate (at the centre of the periphery) and shouldered last whorl. Teleoconch densely spirally striated. Last whorl very slightly detached from the penultimate and with a sharp shoulder. Apertural barriers few (angulo-parietal (parietal), upper palatal, lower palatal and columellar) and relatively weak. Umbilicus initially narrow and then abruptly widening at the last whorl.

Description.

Shell conical or slightly concave-conical, dark brown, consisting of 4–4.5 whorls separated by a deep suture. Protoconch rounded, slightly glossy, roughly pitted, consisting of ~ 1.5 whorls. Initial teleoconch whorls rounded, penultimate whorl bluntly keeled. Teleoconch sculptured with strong, raised spiral striae which are crossed by weaker radial growth lines usually in form of whitish radial streaks. There are ~ 30 spiral striae on the last whorl in standard view. The spacing between two striae ranges to ~ 2–3 × the width of one stria. Basis of the last whorl flat. Last whorl with a sharp shoulder (almost like a keel), adnate or very slightly detached from the penultimate, very slightly descending near the aperture (less than 5 ° compared to the shell axis), almost straight. Peristome brown, not very strong but still expanded and not reflected. Aperture equipped with four main barriers (parietal (angulo-parietal), upper palatal, lower palatal and columellar), none of which reach the expanding peristome. Angulo-parietal lamella is the strongest, longest and the highest in the aperture. There is usually no sign of the angular part. Upper and lower palatal plicae both low and relatively weak, almost equally strong. Basal plica clearly present and moderately strong or absent (with only a slight swelling in its place). Columellar lamella developed to a similar extent as both palatal plicae. There is one additional swelling in the columello-parietal embayment which corresponds to the infraparietal lamella. Surface of all apertural barriers is finely granulated. Sinulus wide and not distinctly separated from the rest of the aperture. Umbilicus initially narrow, but abruptly widening at the last whorl, becoming very wide, and measuring slightly> ½ of the shell width. There is a deep groove running from the peristome edge towards the umbilicus along the inner side of the last whorl. This groove is terminating at the transition from the last whorl to penultimate.

Differential diagnosis.

This species is the most similar to H. geckophilum sp. nov. from which it differs in the more rectangular shape of the last whorl and a stronger shoulder. Umbilicus is also much narrower in H. geckophilum sp. nov. and the barriers are more slender.

Measurements

(in mm, n = 5). SH = 2.36–2.75; SW = 2.56–2.85; AH = 1.20–1.32; AW = 1.25–1.47.

Etymology.

This species is named for the flat base of the shell.

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. platybasis sp. nov., it is possible that this species can be found here as well and be threatened by quarrying.