Acmella thamsingensis Seedee, Dumrongrojwattana & Poeaim, 2025

Seedee, Kunya, Dumrongrojwattana, Pongrat & Poeaim, Supattra, 2025, Four new species of genus Acmella W. T. Blanford, 1869 (Gastropoda, Assimineidae) from Southern Thailand, ZooKeys 1256, pp. 275-292 : 275-292

Acmella thamsingensis Seedee, Dumrongrojwattana & Poeaim sp. nov.

Fig. 5

Type material.

Holotype: Thailand • WatTham Sing , Tham Sing Subdistrict, Mueang District, Chumphon Province; 10.4256, 99.0600; November 2023; Kunya Seedee; deposited in the Malacological Collection; catalog no. ZRCBUU 0989 ; GenBank accession number: PV 157991 , SH = 1.01 mm, SW = 0.81 mm, AH = 0.41 mm, AW = 0.42 mm (Fig. 5 A – E , Table 2 ) . Paratype: Thailand • 4 shells; same locality data as holotype; November 2023; deposited in the same institution as the holotype; catalog no. ZRCBUU 0990 ; GenBank accession number: PV 157992 , SH = 1.37–1.43 mm (1.40 ± 0.03 mm), SW = 0.93–1.03 mm (0.98 ± 0.05 mm), AH = 0.46–0.57 mm (0.49 ± 0.05 mm), AW = 0.37–0.49 mm (0.44 ± 0.06 mm) .

Diagnosis.

Shell shape conical, white; suture visible; whorls 4–6. Aperture oblique oval. The last whorl sculpture consists of a lattice pattern on the upper part of the whorls. Umbilicus open and narrow.

Description.

Shell conical, white, translucent; rounded apex; whorls convex on the side up to a deep suture; 4 ¼ – 6 whorls. The aperture is oblique oval, with a wall next to the upper body, a concave part following the shell shape, and a thin peristome. The umbilicus is open, narrow, and superficial (Fig. 5 A ). Protoconch is a rough sculpture scattered throughout the area up to the second whorl (Fig. 5 B, C ). The last whorl sculpture is a spiral low convex sculpture with 23–26 rows, wide, conspicuous, and regularly spaced with a narrow groove in the wide rows. Radial sculpture tapered in the upper part of the whorl (Fig. 5 D ). Operculum paucispiral, thin, transparent, and composed of chitin (Fig. 5 E ).

Differential diagnosis.

The spiral sculpture of A. thamsingensis sp. nov. is more prominent than that of A. cyrtoglyphe , where it is almost absent. The radial sculpture of A. thamsingensis sp. nov. is limited to the upper part of the whorl, unlike A. cyrtoglyphe , which exhibits a more distinct and complete radial sculpture. Compared to A. krueangensis sp. nov., which has evenly distributed radial sculpture across the shell, A. thamsingensis sp. nov. bears radial elements only on the upper portion of the last whorl. In contrast, A. changphueakensis sp. nov. and A. kanchanaditensis sp. nov. lack radial sculpture.

Etymology.

The specific name thamsingensis refers to Wat Tham Sing, where the species was discovered.

Habitat and distribution.

This species is only found at the study site.

Ecology.

The new species was discovered in aphotic cave zones, inhabiting moist microhabitats where water percolates through the cave walls, approximately 20 m from the entrance.

Figures

Figure 5. Scanning electron micrographs (SEM) of Acmella thamsingensis sp. nov. (A – E) various shell views. A. Overall shell view; B, C. Protoconch and sculpture details; D. Last whorl sculpture; E. Operculum. Scale bars: 0.5 mm (A, B); 0.1 mm (C – E).