Boysidia houaphanica, Inkhavilay & Sutcharit & Chirasak, 2024

Boysidia houaphanica View in CoL , new species

( Figs 2B View Fig , 3 View Fig )

Material examined. Holotype CUMZ 14420 View Materials (height 3.2 mm, width 2.8 mm, 6 whorls; Fig. 3A–C View Fig ) from limestone outcrop at Ban Lao , Samtay District, Houaphanh Province, Laos (20°00′52.4″N, 104°40′57.0″E), coll. K. Inkhavilay, A. Inthavong and C. Oulaiseng, May 2022 GoogleMaps . Paratypes CUMZ 14421 View Materials (6 shells; Figs 2B View Fig , 3D View Fig ) , CUMZ 14422 View Materials (3 shells), and NHMUK (2 shells) were all collected from the type locality together with the holotype .

Diagnosis. Shell minute, heliciform, without tuba. Protoconch sculpture with weakly malleated pits; teleoconch with irregular growth lines. Apertural dentition consisting of five lamellae (parietal, upper and lower palatals, basal and columellar), and small palatal tubercle.

Description. Shell elongate conical, yellowish brown to chestnut-brown, with 5½ to 6¾ convex whorls. Shell height 3.1–3.5 mm, shell width 2.5–2.8 mm. Apex rather round; protoconch about 1½ whorls with weak malleated pits. Teleoconch generally smooth with scattered, prominent and irregular growth lines; suture wide, deeply impressed. Last whorl large, rounded, slightly descending near aperture. Peristome attached to preceding whorl; inner surface including plicae and lamellae covered with scattered small nodules; lip slightly thickened, whitish, broadly expanded. Aperture sub-rectangular, with six apertural teeth. Parietal lamella (p) strongly developed, elevated, sinuous deeply inside aperture, consisting of two parts separated at concrescent point: outer part elevated, strong, curved, reaching peristome margin; inner part thickened, elevated, stronger than outer part. Palatal tubercle (pt) strongly developed with triangular shape. Upper palatal plica (upl) thin, flake shaped, long inside aperture, elevated to nearly touch parietal lamella, forming an almost separate chamber at upper junction of peristome; lower (lpl) palatal strong, elevated. Basal plica (b) prominent, small and low. Columellar lamella (c) large, strong, distinct horizontally. Umbilicus perforate, about one-fourth of shell width, rounded, shallow, not revealing preceding whorl.

Differential diagnosis. Boysidia pahpetensis ( Fig. 2A View Fig ) from Laos differs from the new species in having a conic shell,

four whorls, rounded aperture, small infraparietal lamella, and a concrescent point situated close to the peristome margin ( Ancey, 1881; Inkhavilay et al., 2019). In contrast, the new species possesses an elongate conical shape, five to six whorls, a sub-rectangular aperture, without infraparietal lamella, and a concrescent point situated deeper inside the aperture.

Boysidia robusta Bavay & Dautzenberg, 1912 from Vietnam and Boysidia chiangmaiensis Panha & Burch, 2002 from Thailand differ from the new species in having ovate conic and large shells (height 4–5 mm) with basal plica. In addition, Boysidia robusta also has an ovate aperture, and with small infraparietal lamella and lower basal plica, while Boysidia chiangmaiensis has a rounded aperture ( Bavay & Dautzenberg, 1912; Panha & Burch, 2002a, 2005). In comparison, Boysidia houaphanica , new species, possesses an elongate conical, smaller shell (height 3.1–3.5 mm), subrectangular aperture, and with basal plica.

For further comparison, Boysidia tholos Panha & Burch, 2002b from Thailand can be distinguished from this new species by having a dome-shaped shell, five whorls, rounded aperture, and infrapalatal lamella. In contrast, Boysidia houaphanica , new species has an elongated conic shell, 5–6 whorls, subrectangular aperture, and without infrapalatal lamella ( Panha & Burch, 2002b, 2005).

Etymology. The species name ‘ houaphanica ’ is derived from the type locality, Houaphanh Province, where the type specimens were collected.

Distribution. This species, Boysidia houaphanica , new species, is known only from the type locality in Houaphanh Province, Laos. The snails were found under leaf litter in limestone rock crevices.

Remarks. This new species occurs sympatrically with Bensonella novemdentata . The occurrence of multiple hypselostomatid species in the same locality is not uncommon (e.g., Inkhavilay et al., 2016; Vermeulen et al., 2019; Páll-Gergely & White, 2022; Sutcharit et al., 2023; Jirapatrasilp et al., 2024).