Hypselostoma iunior Gojšina & Páll-Gergely, 2025

Hypselostoma iunior Gojšina & Páll-Gergely sp. nov.

Figs 111 Z View Figure 111 , 148 View Figure 148 , 149 View Figure 149 , 154 View Figure 154

Type material.

Holotype. Thailand • 1 shell (SH: 2.44 mm, SW: 1.70 mm); Nan Province, Pha Tup cave , Ban Pha Tup, 12 km N of Nan; 18°51′0″N, 100°44′9″E; 260 m a. s. l.; 29 Apr. 1988; F. G. Thompson leg.; UF 347376 GoogleMaps . Paratypes. Thailand • 1 shell; same data as for holotype; CUMZ 14454 View Materials GoogleMaps • 3 shells; same data as for holotype; UF 591327 GoogleMaps • 3 shells; Nan Province, Ban Pha Sing , 16 km N of Nan; 18°52′26″N, 100°45′0″E; 270 m a. s. l.; 28 Apr. 1988; F. G. Thompson leg.; locality code FGT-4349 , UF 347358 GoogleMaps .

Additional material examined.

Thailand • 7 shells (juveniles, not paratypes); same data as for holotype; UF 583729 GoogleMaps .

Type locality.

Thailand, Nan Province, Pha Tup cave, Ban Pha Tun, 12 km N of Nan; 18°51′0″N, 100°44′9″E; 260 m a. s. l.

Diagnosis.

Hypselostoma with very dense spiral striation on the teleoconch. Apertural barriers very weak and four (parietal, upper palatal, lower palatal and columellar). Umbilicus narrow, widening at the last whorl.

Description.

Shell conical, light yellow to brown, consisting of 5–5.5 convex, rounded whorls separated by a deep suture. Protoconch slightly lighter than the rest of the shell, consisting of ~ 1.5 whorls, densely spirally striated (striae clearer terminally). Teleoconch very finely, densely spirally striated crossed by stronger and much coarser, irregularly spaced radial growth lines. Last whorl rounded to slightly shouldered, adnate to the penultimate and slightly to moderately descending (~ 25–35 ° compared to the shell axis) making the aperture profile prosocline to the shell axis. Peristome white but not much expanded, not reflected. It is only particularly expanded on the columellar side where it forms a strong margin which is, however, not covering the umbilicus. The peristome is discontinuous on the parietal side where it is completely merged with the penultimate whorl. Aperture almost as wide as high. Apertural barriers few and much weaker than in the majority of congeners. There are four barriers: parietal, upper palatal, lower palatal and columellar. Parietal lamella is the strongest in the aperture but still somehow weak, moderately high and curved towards the palatal side. Two palatal plicae (upper and lower palatal) are very weak, like small thickenings. Columellar lamella also weak and shares the same appearance as the palatal plicae but situated slightly closer to the peristome edge. None of the apertural barriers are reaching the thin peristome. Surface of all apertural barriers is almost smooth but very finely granulated. Sinulus wide and not strongly isolated from the rest of the aperture. Umbilicus moderately wide, measuring 1 / 5 of the shell width, initially narrow and suddenly widening at the last whorl (which gives it a slightly elongated appearance).

Differential diagnosis.

This species is similar to A. eotvosi with which is also geographically adjacent. It differs by the much larger sizes in A. eotvosi , narrower umbilicus and the lack of spiral striation. The shell of A. eotvosi is also more pointed, especially near the apex. See also under H. panhai .

Measurements

(in mm, n = 6). SH = 2.27–2.48; SW = 1.67–1.72; AH = 0.81–0.92; AW = 0.84–0.96.

Etymology.

This species is named iunior for the very weak teeth and weakly expanded peristome which is common in subadult hypselostomatid specimens.

Distribution.

This species is known only from its type locality.

Remarks.

Since the most similar species ( H. panhai ) belongs to the genus Hypselostoma (as shown in a phylogenetic study by Tongkerd et al. 2004), this species is also included in this genus even though it fits in the diagnosis of Anauchen .