Chamalycaeus buaboke Pall-Gergely & A. Reischutz 2021, n. sp.

Chamalycaeus buaboke Páll-Gergely & A. Reischütz n. sp.

Figs 1A, 2

Material examined. Holotype: Thailand, Surat Thani Province, Ang Thong Islands, Wua Talap Island, ascent to Buaboke Cave, 9°37.993’N, 99°40.369’E, ca. 50 m a.s.l. (locality code: Th1), Sep. 2007, A. Reischütz leg., at base of limestone rocks, NHMW 113484 (D: 2.03 mm, H: 1.23 mm). Paratype: 1 shell, same data as holotype, RE.

Etymology. The specific epithet (noun used in apposition) derives from the name of the cave where the new species was collected.

Diagnosis. A tiny Chamalycaeus species with finely ribbed R1, elevated, narrow swelling on R3, and great distance between inner and outer peristomes.

Description. Shell off-white, probably somewhat translucent when fresh; shell outline oval in dorsal view; spire slightly elevated, low conical; body whorl rounded; protoconch low, finely granular, spiral striae lacking, 1.25–1.5 whorls; R1 of 1.25–1.5 whorls, with strong, elevated, slim, densely, regularly arranged ribs, fine spiral striation between ribs; boundary between R1 and R2 distinct due to change of rib density; R2 ribs slightly curved towards aperture, spaces between ribs approximately as wide or slightly wider than ribs; ca. 26 ribs present; R2+R3 less than quarter whorl (ca. 80˚), R2 somewhat shorter than R3; boundary between R2 and R3 distinct due to deep constriction and ribless posterior portion of R3; R3 with short, narrow, ribbed central swelling; anterior slope of swelling steeper than posterior slope; aperture oblique to shell axis, rounded with small basal incision; boundary between inner and outer peristomes conspicuous, inner peristome strongly thickened, protruding, and slightly expanded; outer peristome thin, strongly expanded, distinctly reflected portion over umbilicus; distance between inner and outer peristomes significant, swelling of R3 and edge of outer peristome closely situated; umbilicus relatively narrow, ca. one fourth of shell width.

Measurements. D: 2.03–2.29 mm, H: 1.23–1.33 mm.

Operculum. Unknown.

Differential diagnosis. The most similar species is Chamalycaeus canaliculatus (Möllendorff, 1894) (examined material: Golf von Siam: Koh-Samui, coll. Möllendorff, SMF 109468, lectotype, Fig. 1B), which was described from the nearby island, Koh Samui. The new species from Wua Talap Island is slightly smaller (C. canaliculatus D: 2.4 mm), has a more elevated R3, and much greater distance between the inner and outer peristomes.

The new species differs from Dicharax ovatus n. sp. by the slightly smaller size, lower spire, very rounded body whorl and aperture, blunt swelling on R3, and the shorter distance between the inner and outer peristomes.

Distribution. This new species is known only from the type locality (Fig. 3).