Hypselostoma pongrati Tanmuangpak & S. Tumpeesuwan, 2025

Hypselostoma pongrati Tanmuangpak & S. Tumpeesuwan sp. nov.

Figs 2 A, B View Figure 2 , 3 A – I View Figure 3 , 5 A – E View Figure 5 , 6 A, B View Figure 6 ; Table 2 View Table 2

Hypselostoma sp. – Tanmuangpak & Kaewsawang, 2025: 20, 23, 25, 27, 29–31, fig. 2 q.

Material examined.

Holotype: Thailand • 1 empty shell; Nong Bua Lamphu Province, Sri Bun Rueang District, Pha Sam Yod limestone hill ( 17°10'02.020"N, 102°02'03.020"E) covered by mixed-deciduous forest; 20.xi.2021, leg. Tanmuangpak, K. ( NHLRU 014 ) (Fig. 3 A – E View Figure 3 ) GoogleMaps . Paratypes: Thailand • 12 specimens preserved in 70 % ethanol ( NHLRU 015–026 ) GoogleMaps ; • five shells ( NHLRU 027–031 ) GoogleMaps ; • three specimens preserved in 70 % ethanol ( NHMSU –00063–B ) GoogleMaps ; • two shells ( NHMSU –00063 ). All paratypes collected from the same location as holotype, leg. Tanmuangpak, K. 10.xii.2021 GoogleMaps .

Measurements.

Holotype: SH = 4.48 mm, SW = 3.34 mm, AH = 1.95 mm, AW = 1.92 mm. Paratypes ( 19 specimens measured): SH = 4.48–6.02 mm (5.58 ± 0.42 mm), SW = 3.07–4.12 mm (3.72 ± 0.36 mm), AH = 1.95–2.64 mm (2.24 ± 0.20 mm), AW = 1.68–2.42 mm (1.99 ± 0.16 mm) (Fig. 7 View Figure 7 ).

Diagnosis.

This new species has a prominent keel on the upper part of the last whorl and a weaker keel on the lower part. Apertural barriers absent (Fig. 3 A, G, H, L View Figure 3 ). Terminal part of the last whorl is adnated to penultimate whorl.

Description.

Shell (Fig. 3 A – I View Figure 3 ) concave-conical, high spired, with 4 ¾ whorls. Large size for the genus, with shell height 4.48–6.02 mm, shell width 3.07–4.12 mm. The suture is deep. Protoconch smooth, with 1–1 ½ whorls that gradually increase in size to the teleoconch whorls. Teleoconch with 3–3 ¾ whorls, very fine spiral striation the body whorl widest, possesses two keels (upper one more prominent than the lower one). Apertural barriers absent. Peristome thickened and expanded. The parietal and convex angulo-palatal embayments form a sinulus, thickened, and expanded. The basal peristome is smooth and expanded, columellar side is more expand than the angulo-palatal side.

Genital system (Fig. 6 A, B View Figure 6 ). Atrium shorter than the vagina. Penis shorter than the epiphallus, its anterior portion is a short and bulged tube, and the distal end of the penis bulge. Epiphallus connects to the distal end of the penis, shorter than vas deferens, anterior portion slender and cylindrical, its central portion more slender than the anterior portion, posterior portion curved, white glossy. Penial retractor muscle absent. Vas deferens long, slender, entering the epiphallus apically. The vagina and free oviduct are cylindrical, and the vagina is shorter than the free oviduct. The gametolytic sac is a long tube, with a swollen proximal part, and larger than penis, surrounded by a thin sheath and connected to the proximal part of the vagina, whose distal end is long, slender, and curved. Uterus large, with very thin prostate gland attached to it. Hermaphroditic duct loosely convoluted. The albumen gland large and yellowish. Dart apparatus absent.

Radula ( n = 4) (Fig. 5 A – E View Figure 5 ). Radula comprises 173–184 (179 ± 4.93) transverse rows of teeth each row containing 25–27 teeth. Radula formula (7-8) + 5 + 1 + 5 + (7-8). Central tooth small, unicuspid, elongated triangular. Lateral teeth bicuspid and asymmetrical, consisting of a large lanceolate endocone and smaller elongated triangular ectocone. Five lateral teeth on each side of the central tooth, the first tooth largest, and gradually smaller outwards. Marginal teeth start at 6 th tooth outwards from central teeth, which almost changed to tricuspids. On each outer side of the lateral teeth there are seven or eight marginal teeth.

Etymology.

This new species is dedicated to the late Pongrat Dumrongrojwattana, our highly respected senior who was an expert on microsnails and who provided us with many land snails references, knowledge, and inspiration.

Animal and ecology.

Living animals have a cream-colored body and foot, while their head and tentacles are rather black, with black eyes located at the tip of the ocular tentacle. This species was found on the limestone wall in the mixed-deciduous forest (Fig. 2 A, B View Figure 2 ).

Distribution.

This species was found only on limestone wall in Pha Sam Yod, Si Bun Rueang District, Nong Bua Lamphu Province.

Remarks.

Hypselostoma pongrati sp. nov. from Si Bun Rueng District, Nong Bua Lam Phu Province, is quite different in shell shape from almost all other Hypselostoma species in Thailand. It is similar in shell shape to the geographically close H. phupaman from Chaiyaphum Province and H. sichomphuense sp. nov. from Si Chomphu, Khon Kaen Province. The unique characteristics of H. pongrati sp. nov. are the lack of apertural barriers and the last whorl adnate to the penultimate whorl, peristome thick, expanded and not reflected. It is strongly expanded at the parietal side where it leans against penultimate whorl and forms a thick crescent callus. Three species possess a double-keeled last whorl, but the lower keel is weak in both H. pongrati sp. nov. and H. sichomphuense sp. nov. Other similar species are H. torta from Nakhon Sawan Province, Thailand and H. platybasis from Steung Treng Province, Cambodia ( Gojšina et al. 2025). In H. torta and H. pongrati sp. nov. all teleoconch whorls are shouldered, but in H. torta the last whorl is detached from the penultimate whorl. There are four weak apertural barriers. The columellar barriers form as a rather strong swelled part of the aperture which forms a prominent basal furrow below it. Hypselostoma platybasis differs from H. pongrati sp. nov. by possesses bluntly keeled penultimate at the center of the periphery and shouldered last whorl. Last whorl very slightly detached from the penultimate whorl and with a sharp shoulder. Apertural barriers few and relatively weak. In H. pongrati sp. nov. there is no penial retractor muscle, and the free oviduct is longer than the anterior portion of the gametolytic sac. Conversely, in H. sichomphuense sp. nov. there is a penial retractor muscle, and the free oviduct is shorter than the anterior portion of the gametolytic sac.