Hypselostoma vicinum Gojšina, Auffenberg & Páll-Gergely, 2025

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

Figs 186 R View Figure 186 , 219 View Figure 219 , 220 View Figure 220 , 223 View Figure 223

Type material.

Holotype. Thailand • 1 shell (SH: 1.9 mm, 2.6 mm); Suratthani Province , limestone outcrop along Hwy. 401, 2.7 km W junc Hwys. 4142 & 401, evergreen forest on rocky hillside, below cliff, base of cliff; 9°10'N, 99°40'E; 90 m a. s. l.; 18 Apr. 1988; K. Auffenberg leg.; UF 345327 . GoogleMaps

Paratypes. Thailand • 1 shell; same data as for holotype; CUMZ 14468 View Materials GoogleMaps • 51 shells; same data as for holotype; UF 591363 GoogleMaps • 45 shells; same data as for holotype; locality code KA-0674 , UF 345336 GoogleMaps • 16 ethanol-preserved specimens; same data as for holotype; locality code KA-0673 , UF 345328 GoogleMaps .

Additional material examined.

Thailand • 12 shells (apical whorls / juveniles, not paratypes); same data as for holotype; UF 583724 GoogleMaps • 3 shells (juveniles / damaged, not paratypes); same data as for holotype; locality code KA-0674 ; UF 583725 GoogleMaps .

Type locality.

Thailand, Suratthani Province, limestone outcrop along Hwy. 401, 2.7 km W junc Hwys. 4142 & 401, evergreen forest on rocky hillside, below cliff, base of cliff; 9°10'N, 99°40'E; 90 m a. s. l.

Diagnosis.

A Hypselostoma species with roughly granulated (not spirally striated) teleoconch, and keeled, detached, and ascending last whorl. Apertural barriers few (five main ones and usually three smaller ones).

Description.

Shell depressed, concave-conical (due to the strongly enlarged last whorl), chestnut brown and weakly glossy, consisting of 3.75–4.25 convex whorls separated by a deep suture. Protoconch is of the same colouration as the teleoconch, finely pitted and showing no spiralling pattern. Boundary between the protoconch and the teleoconch not clear under microscope because of the very similar surface sculpture of the two regions, but the former is ~ 1.5 whorls. Teleoconch roughly granulated (sandpaper-like), weakly sculptured with radial growth lines but devoid of spiral striation (these radial lines are much harder to observe than the prominent granulation). Occasionally, thicker whitish radial streaks are unevenly placed across the surface of the shell. Last whorl with a very blunt keel (which is getting stronger near the aperture) positioned at the centre of the periphery. Shell surface is immediately below and above the keel concave, and then again convex towards the suture and the umbilicus. Last whorl is also very slightly detached from the penultimate and moderately ascending upwards (~ 40–50 ° compared to the shell axis). Peristome dirty white, expanded but not reflected, its surface very finely pitted. There are altogether five main apertural barriers (angular, parietal, upper palatal, lower palatal and columellar) and several smaller ones of variable number. Parietal lamella is the strongest and highest in the aperture, straight but directed towards the palatal side. Angular lamella ~ 2 × lower and shorter than the parietal, but extends closer to the expanding peristome, almost reaching it. Upper and lower palatal plicae almost the same in height and length, the former may be slightly weaker than the latter. Columellar lamella horizontal, almost identical to the lower palatal plica. Among the smaller barriers, there is usually one interpalatal plica which is very small, dot-like. Slightly larger basal plica is present nearly halfway between the lower palatal and columellar. One dot-like swelling is present in the columello-parietal transition embayment. Surface of all apertural barriers is very finely spiniferous medially and very finely granulated laterally. Sinulus wide, not distinctly separated from the rest of the aperture. Umbilicus wide, measuring slightly> 1 / 4 of the shell width. A shallow groove runs alongside the umbilicus but is visible only around the last quarter of the last whorl.

Differential diagnosis.

Less depressed forms of H. fortunatum sp. nov. can resemble this species but the barriers in the former are much weaker and angular and parietal lamellae are concrescent. See also under H. troglodytes .

Measurements

(in mm, n = 5). SH = 1.73–2.06; SW 1 = 2.49–2.85; SW 2 = 1.63–1.79; AH = 0.93–1.19; AW = 0.94–1.10.

Etymology.

The specific epithet vicinum comes from the Latin word for neighbour. This name is provided because the most similar species to the new one, H. troglodytes, lives in the neighbouring Peninsular Malaysia.

Distribution.

This species is known only from the type locality.