Tricula viengthongensis, Grego, Jozef, 2018

Grego, Jozef, 2018, First record of subterranean rissoidean gastropod assemblages in Southeast Asia (Mollusca, Gastropoda, Pomatiopsidae), Subterranean Biology 25, pp. 9-34 : 27-28

Tricula viengthongensis sp. n. Figs 45-48

Type locality.

Laos; Bolikhamsay Province, 16 km West of Vieng Thong, 500 m North of the road from Vieng Thong to Ban Samsok Noy (and Sôp Sang), unnamed cave with entrance above large karst spring with travertine cascades (Fig. 2D), 18°34.080'N; 104°31.79'E, sand sediments on the bottom of cave rivulet.

Type material.

Holotype: type locality: J. Grego and B. Šmída leg. 19 February 2017 (NHMUK 20180015) Paratypes:, type locality (coll. Grego F0904 - 3 specimens).

Measurements.

Holotype: H 2.64mm; W 1.64mm; BW 0.93mm; BH 1.71mm; AH 1.14mm; AW 1.00mm; H/W 1.6; AH/AW 1.14; W/BW 1.76; H/BH 1.54; H/AH 2.32; W/AW 1.64.

Diagnosis.

The small conical shell is similar to that of T. valenasi sp. n. (Khammouane Province) from which it differs by its smaller size and its more blunt apex. From T. lenahani sp. n. (Khammouane Province) it differs by having a smaller shell with a weaker suture and a closed umbilicus. Tricula phasoungensis sp. n. and T. bannaensis sp. n. have a more robust and rounded shell with more convex whorls and an open umbilicus.

Description.

The shell of Tricula viengthongensis sp. n. is whitish, semi-translucent with four slightly flattened convex whorls and a weak suture. The shape of the shell is conical with a blunt apex and an oval ear shaped aperture. The marginal lips with a slight callosity are not reflexed and laterally have a straight profile without any sinuation. The umbilicus is closed.

Etymology.

Named after the city of Vieng Thong (Bolikhamsay Province), the larger settlement closest to the type locality.

Distribution.

Only known from the type locality.

Ecology.

The unnamed cave is situated immediately above a large karstic spring with travertine cascades (fig. 2D), and drains a limestone ridge NW of the main water outlet. The cave entrance is a 15m vertical abyss continuing upstream the underground river to a siphon lake. The total length is approximately 400 m with several parallel draining passages. The specimens were collected from sandy sediment at the bottom of a cave stream about 40 m upstream from the entrance.