Hypselostoma fungus Gojsina, Hunyadi & Pall-Gergely 2025, sp. nov.

Hypselostoma fungus Gojšina, Hunyadi & Páll-Gergely sp. nov. Figs 111 V, 141, 142, 177 Material examined. Holotype. Cambodia • 1 shell (SH 2: 2.94 mm; SW: 3.09 mm); Steung Treng Province, 36.3 km northwest and 5 km north from Stung Treng Mekong Bridge, Phnom Chhnok; 13°46.573'N, 105°44.878'E; 120 m a. s. l.; 25 Oct. 2023, A. Hunyadi & J. U. Otani leg.; CUMZ 14453. Paratypes. Cambodia • 219 shells; same data as for holotype; coll. HA • 1 shell; same data as for holotype; coll. VG. Additional material examined. Cambodia • 3 shells (broken, not paratypes); same data as for holotype; coll. HA. Type locality. Steung Treng Province, 36.3 km northwest and 5 km north from Stung Treng Mekong Bridge, Phnom Chhnok; 13°46.573'N, 105°44.878'E; 120 m a. s. l. Diagnosis. Hypselostoma species with a large last whorl (previous whorls sunken into it) and spirally striated teleoconch. Last whorl strongly detached from the penultimate and descending at almost 80 ° compared to the shell axis. Aperture equipped with four main barriers (angulo-parietal, upper palatal, lower palatal and columellar) and some smaller ones. Basal furrow present. Umbilicus extremely wide, almost as wide as the whole shell. Description. Shell depressed-conical, brown, and not glossy, consisting of 3.5–4 whorls separated by a deep suture. Protoconch rounded, roughly pitted and consisting of one whorl. Initial teleoconch whorls bluntly keeled and sunken into the last whorl (but sometimes they appear more elevated). Last whorl contributing to almost 100 % of the shell height. It is extending obliquely around the previous whorls and is strongly shouldered both on its upper and lower sides, which gives the shell a unique appearance. Surface of the teleoconch is irregularly, very finely and densely spirally striated. Whitish radial streaks are numerous and present on all teleoconch whorls but unevenly spaced (rather randomly positioned). Last whorl is strongly detached from the penultimate and strongly descending (~ 80 ° compared to the shell axis). This makes the aperture profile almost perpendicular to the shell axis. The so called “ trumpet ” is quite broad (similar to e. g., H. chaunosalpinx). Peristome is dirty white (or light brown), thick and strongly expanded, not reflected. Aperture is equipped with four main barriers (angulo-parietal, upper palatal, lower palatal and columellar) and additional smaller ones. The parietal part of the angulo-parietal lamella is strong and very high (blade-like), but the angular is very short and pointed towards the palatal side. Upper palatal plica is directed towards the lower palatal plica but is weaker. Lower palatal plica is long and low in its inner part and much higher in its outer part (closer to the peristome). This plica is similar to the columellar lamella but more slender. Basal (?) plica is situated closer to the lower palatal. It is not clear whether this plica actually represents the infrapalatal or the basal. In the region where usually the basal plica is present, there is a deep basal furrow which is also rarely encountered in this group (similar structure is also present in H. torta sp. nov.). This furrow is stretching all the way to the expanding peristome. Columellar lamella almost horizontal, thick, and long. A distinct infraparietal lamella is present (sometimes absent) between the columellar and parietal lamellae. Of all these barriers, only the angulo-parietal and columellar lamellae are reaching the expanding peristome. Surface of all apertural barriers is finely granulated. Sinulus narrow, well separated from the rest of the aperture. Umbilicus extremely wide (almost as wide as the whole shell). The lower edge of the last whorl (towards the umbilicus) is very strongly ridged (almost forming a cliff-like structure), leaving the walls of the umbilicus very steep (like a playground slide). The walls of the umbilicus are especially densely sculptured with white radial streaks. Differential diagnosis. See under H. srakeoense, H. pendulum, H. torticollis, and H. transitans. Measurements (in mm, n = 5). SH 1 = 2.83–2.97; SH 2 = 1.62–1.85; SW = 3.09–3.85; AH = 1.82–2; AW = 1.77–2.05. Etymology. This species’ shape resembles a mushroom, which gave its specific epithet (Lat. fungus). The detached last whorl resembles a stalk while the rest of the shell resembles a cap. To be used as a noun in apposition. Distribution. This species is known only from its 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. fungus sp. nov., it is possible that this species can be found here as well and be threatened by quarrying.