Amphidromus (Syndromus) principalis Sutcharit & Panha

Sutcharit, Chirasak, Ablett, Jonathan, Tongkerd, Piyoros, Naggs, Fred & Panha, Somsak, 2015, Illustrated type catalogue of Amphidromus Albers, 1850 in the Natural History Museum, London, and descriptions of two new species, ZooKeys 492, pp. 49-105 : 82-84

Taxon classification Animalia Stylommatophora Camaenidae

Amphidromus (Syndromus) principalis Sutcharit & Panha sp. n. Figs 16B, J–L, 17C, D

Type material.

Holotype: CUMZ 2543 (height 33.9 mm, width 17.9 mm, whorls 6; Fig. 16J), paratypes CUMZ 2478 (3 shells, Fig. 16K, L), CUMZ 2386 (19 shells), CUMZ 2387 (18 shells), NHMUK 20140708 (2 shells) and SMF (2 shells).

Measurement of 27 paratypes; height range 25.2-36.0 mm, mean 30.60 ± 2.38; width range 14.5-18.9 mm, mean 16.43 ± 1.09; height/width ratio 1.69-2.00, mean 1.86 ± 0.07; whorls 5¾–6¾.

Other material.

From the type locality CUMZ 2401, 2422.

Type locality.

Koh Kra, about 30 km off the east coast of Pak Phanang, Nakhon Srithammarat in the Gulf of Thailand (8°23'55"N, 100°44'2"E).

Diagnosis.

This new species is distinguished from Amphidromus globonevilli Sutcharit and Panha, sp. n. by having a more ovate to elongated conic shell of entirely uniform bright yellow colour. The reproductive organ lacks a vaginal pouch, the penial verge is small and conical. Living snails have an entirely whitish to creamy body; only older snails are likely to have a pale brown head-foot. Superficially, this new species resembles Amphidromus flavus from northern Thailand and Laos. However, this new species exhibits a bright yellow, slightly ovate shell, shorter expanded lip and thickened shell, while Amphidromus flavus has a slender, pale yellow shell, wide expanded lip with faint spiral band below periphery (Fig. 7I, J).

Description.

Shell. Shell ovate to slightly elongate conic, glossy, smooth, sinistral and rimate. Apex obtuse with brown to black spot on the tip. Shell uniform golden yellow (without any bands). Last whorl darker yellow than earlier whorls. Spire conic with slightly depressed suture. Aperture ovate; peristome white, narrowly expanded and not reflected. Columella white, straight and perpendicular. Parietal callus thin and translucent.

Genital organ.

Atrium (at) slightly long (n = 10). Penis (p) long, cylindrical and enlarged in middle. Epiphallus (e) longer than penis length; flagellum (fl) shorter than epiphallus; appendix absent. Penial retractor muscle (pr) thickened and relatively long (Fig. 17C). Vas deferens (vd) small tube and connected between epiphallus and free oviduct.

Internal wall of penis corrugated into series of thin and longitudinal penial pilasters (pp), which form a thin fringe around penial verge. Penial verge (pv) short conic, surface with thin irregular furrow (Fig. 17C).

Female reproductive organ similar to former described species but differs in that vagina internal wall possesses swollen and nearly smooth longitudinal vaginal pilaster (Fig. 17C, D).

Etymology.

The specific epithet is derived from the Latin " principalis " meaning “leader” and refers to Her Royal Highness Princess Maha Chakri Sirindhorn who chaired the Plant Genetic Conservation Project as a Royal Initiation to support biodiversity in Thailand. The malacological survey on Koh Kra in 2000 was part of an expedition supported by this project.

Distribution.

This new species is known only from the type locality.

Remarks.

Amphidromus principalis Sutcharit & Panha, sp. n. is known only from the type locality, the granitic island. The forestation type on the island was dry evergreen forest, the snails were found crawling on the tree leaves, trunks or branches of almost all trees up to 10 m height. We also explored two other satellite islands but found no Amphidromus on these islands or any other terrestrial snails other than subulinids.