Landouria flagellolonga Nahok & K. Tanmuangpak sp. nov.

Figs 3 B, 7 –9; Table 2

Landouria sp. 10 — Nahok 2020: 55; figs 24 A, 33; table 3.

Type locality.

Thailand, Sa Kaeo Province, Khlong Hat District, Phet Pho Thong Cave, 13°24'52.89"N, 102°19'31.03"E, limestone hill, alt. 236 m, 15 Oct. 2017, Benchawan Nahok and Utain Chanlabut leg.

Type specimens.

Holotype: ZCPRU -0048 (Fig. 7), SH = 6.80 mm, SW = 9.65 mm. AH = 4.72 mm, AW = 3.60 mm. Paratypes: ZCPRU -0049 30 shells, ZCPRU -0050 (Fig. 3 B), 12 living specimens preserved in ethanol, same collector and locality as holotype, 27 Aug. 2025.

Diagnosis.

Shell small, light brown-corneous, sharply keeled. Flagellum very long, epiphallus long and slender; penis long, cylindrical, dilated at its middle part; vagina and free oviduct short. Radula with lanceolate central and lateral teeth.

Description.

(empty shells = 31, living specimens = 12) Shell (Fig. 7) dextral, small, conical-lenticular, SH = 5.90 – 7.50 mm (6.70 ± 0.46 mm), SW = 8.20–11.10 mm (9.65 ± 0.84 mm), AH = 3.50–5.30 mm (4.40 ± 0.52 mm), and AW = 3.50–5.00 mm (4.25 ± 0.43 mm), with 6–6.25 slightly convex whorls. Protoconch almost smooth. Teleoconch with irregular wrinkles; incised spiral lines not discernible. Apex obtuse and depressed. Suture shallow. Body whorl sharply keeled. Umbilicus open, relatively wide (occupying c. 1 / 3 of SW). Aperture rounded rhombic; apertural lip reflexed and thickened.

Genital system (N = 3) (Fig. 8). Atrium short. Dart apparatus and mucous glands absent. Penis twice as long as epiphallus, long, cylindrical, broad in middle and narrows at distal end, internally with five narrow longitudinal pilasters, without a verge (Fig. 8 C, D). Epiphallus divided into two somewhat identical parts; proximal part (ep 1) connected to penis, slightly larger and longer than distal part (ep 2). Penial retractor muscle present. Flagellum very long, without node, tapering towards its distal end, internally with a few fine longitudinal folds (Fig. 8 G, H). Vas deferens thin and long. Vagina approximately 1 / 2 of penis length, internally with six smooth, longitudinal pilasters (Fig. 8 E, F); free oviduct short, regularly cylindrical tube. Gametolytic sac slightly thicker at base, with long, narrow, thin cylindrical tube, and at its distal end, a small, swollen spherical sac. Prostate gland very long. Uterus long and thin.

Radula (N = 3) (Fig. 9). Comprises 121–125 transverse rows with 53–61 teeth per row, formula: (17–19) + (9–11) + 1 + (9–11) + (17–19). Central tooth usually symmetric, unicuspid, lanceolate (Fig. 9 B). Lateral teeth unicuspid, elongate-lanceolate, oblique, and longer than central teeth (Fig. 9 B). Marginal teeth gradually changing from unicuspid to bicuspid and finally tricuspid (Fig. 9 C – F).

Etymology.

Specific epithet derived from Latin word longus, meaning “ long ” and referring to the elongated flagellum of this species.

Habitat.

This species inhabits limestone hills with scattered outcrops, bare ground, and trees in a natural forest.

Distribution.

Landouria flagellolonga sp. nov. is known from the surroundings of limestone hills at Phet Pho Thong Cave, Khlong Hat District, Sa Kaeo Province, eastern Thailand (Fig. 1).

Remarks.

Landouria flagellolonga sp. nov. differs from other Thai species of Landouria by its genital system, which has the most slender and longest flagellum (Fig. 8).