Diplommatina somsakpanhai Tongkerd 2026, sp. nov.

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7Diplommatina somsakpanhaiTongkerd sp. nov. Figs 11 C, 13 Type material. Myanmar • Holotype. CUMZ 15460 (height 1.4 mm, width 2.2 mm; Fig. 13 A) from Buddha Cave, Lenya City, Tanintharyi Region; 11°13'46.2"N, 99°10'34.3"E, 65 m a. s. l.; C. Sutcharit, R. Chanabun and R. Srisonchai leg. • Paratypes. CUMZ 15461 (6 shells; Figs 11 C, 13 B) and CUMZ 15462 (30 shells + 20 juveniles); same data as for holotype. • NHMUK 20260057 (5 shells); same data as for holotype. • SMF (5 shells); same data as for holotype. Diagnosis. Shell small, sinistral, ovoid fusiform, ~ 5 ½ rounded whorls. Last whorl nearly same diameter as penultimate whorl. Shell with narrowly spaced radial ribs, fine spiral striations throughout. Peristome thickened, double, broadly expanded. Aperture rounded, with three barriers: parietalis, palatalis and columellaris. Description. Shell sinistral, ovoid-fusiform, pale orange or light yellowish. Shell height 1.3–1.5 mm; shell width 2.1–2.2 mm. Whorls ~ 5 ½, rounded; spire depressed conic; suture wide, deep. Protoconch ~ 1 ¾ whorls, nearly smooth to very weakly wrinkled or with roundish pits. Teleoconch with regular and narrowly spaced radial ribs; ribs spaced slightly wider near aperture; 10–11 ribs / 0.5 mm on penultimate whorl, 7–8 ribs / 0.5 mm on last whorl towards aperture. Spiral striations very fine, weakly appearing throughout. Last whorl slightly narrower than penultimate whorl. Constriction externally inconspicuous; internal constriction marked with indistinct vertical ridge. Aperture circular with three barriers: parietalis and palatalis weak, low ridges; columellaris distinctly prominent ridge, continuous with peristome, slightly deflected downward toward palatal wall (Fig. 11 C). Peristome double, broadly expanded, and nearly or completely reaches suture; inner peristome broader than outer peristome. Lip thickened, multi-layered; parietal callus thickened, broadly expanded. Columella thickened and curved. Umbilicus sealed. Differential diagnosis. Diplommatina somsakpanhai sp. nov. can be distinguished from D. siriphumi Panha & Burch, 2001 from Chiang Mai Province, Thailand, by several diagnostic characters. The new species possesses more ovate whorls, a narrow space between radial ribs, a broadly expanded peristomal lip, and a large, distinct columellaris. In contrast, D. siriphumi (Fig. 7 D) has a less ovate whorl, a wide space between radial ribs, a narrow peristomal lip, and a small, less prominent columellaris. In addition, D. siriphumi was recorded from a non-limestone habitat located approximately 700 km north of the type locality of this new species (Panha and Burch 2001, 2005). Furthermore, the new species differs from Pagodapalaina krabiensis (Panha & Burch, 1998) from southern Thailand by its ovate-fusiform shell, ovate whorls, narrowly spaced radial ribs, and broadly expanded peristomal lip. In comparison, P. krabiensis possesses a fusiform shell with shouldered whorls, widely spaced radial ribs, and a narrowly expanded peristomal lip (Panha and Burch 1998, 2005). Distribution. Diplommatina somsakpanhai sp. nov. is currently known only from its type locality in the Tanintharyi Region, Myanmar. It inhabits limestone cliff faces and rock crevices, with surrounding vegetation (Fig. 1 A). Etymology. The specific name somsakpanhai is derived from the full name of Professor Dr. Somsak Panha of Chulalongkorn University, in recognition of his remarkable contributions to the study of Southeast Asian land molluscs and biodiversity research in Thailand. This new species is named in his honour to celebrate the anniversary of his sixty-fifth birthday. Remarks. This new species is superficially similar to the type species of Gastroptychia, G. adversa (Adams & Adams, 1851), in having a sinistral, ovate-fusiform shell and a strongly expanded lip that is nearly attached to the suture (Adams and Adams 1851; Vermeulen 1993: 36, fig. 42). Although Gastroptychia has recently been resurrected as a valid genus, its diagnostic characters and distribution remain intermixed with the highly diverse genus Diplommatina, and the characters supporting its separation are still provisional (Egorov 2013; Chen and Ablett 2024). Current recognition of Gastroptychia is mainly based on molecular phylogenetic evidence (Webster et al. 2012), but this analysis did not include the type species. Therefore, in the absence of clear generic diagnostic characters, we provisionally place this new species in the widespread genus Diplommatina, pending a clearer definition of the diagnostic characteristics of Gastroptychia. There are very few sinistral Diplommatina species that have been recorded from Myanmar, only five of 31 known species that occur in Myanmar, namely D. salwiniana, D. scalaroidea, D. akron, P. suratensis, and the new species described herein.

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Related topics: Diatoms and Algae Research · Subterranean biodiversity and taxonomy · Mollusks and Parasites Studies