Alycaeus senyumensis, Foon, Junn Kitt & Liew, Thor-Seng, 2017

Foon, Junn Kitt & Liew, Thor-Seng, 2017, A review of the land snail genus Alycaeus (Gastropoda, Alycaeidae) in Peninsular Malaysia, ZooKeys 692, pp. 1-81 : 44

Alycaeus senyumensis sp. n. Figures 7 V–W, 28, 31R

Alycaeus kelantanensis : Clements et al. 2008: 2760.

Type locality.

PHG 02 Gunung Senyum, Pahang (3°41'50"N, 102°26'04"E).

Type material.

Holotype. PHG 02 Gunung Senyum, Pahang: BOR/MOL 12965. Paratypes. PHG 02 Gunung Senyum, Pahang: BOR/MOL 6880/2, BOR/MOL 12966/69. PHG 03 Gunung Jebak Puyuh, Pahang: BOR/MOL 8395/6, BOR/MOL 12964/2.

Other examined materials.

PHG 02 Gunung Senyum, Pahang: BOR/MOL 275/1, BOR/MOL 6195/6, BOR/MOL 6239/4, BOR/MOL 6249/11, BOR/MOL 8391/41, BOR/MOL 8392/29, ZRC 1975.2.22.444-543/100, ZRC 1975.2.22.626-632/7. PHG 03 Gunung Jebak Puyuh, Pahang: BOR/MOL 6630/13, BOR/MOL 8394/27.

Etymology.

Named after the type locality, Gunung Senyum.

Description.

Protoconch. Smooth.

Shell shape. Conical. Shell height: 4.49-5.01 mm. Shell width: 3.96-4.41 mm.

Spire. Spire height: 1.47-1.94 mm. Spire width: 2.05-2.28 mm. Number of whorls: up to 5 ¼. Spire shape: oblong conical. Whorl periphery rounded. Umbilicus partially closed.

Whorl constriction. At about 5 whorls posterior of protoconch.

Breathing tube. Length: 0.44-0.57 mm.

Aperture and peristome. Aperture circular, very expanded especially at columellar section. Aperture height: 2.17-2.36 mm. Aperture width: 2.02-2.20 mm. Peristome double, thickened, upper palatal section folded posteriorly into a wing-like structure, notched at suture. Peristome orientation 21-28° oblique with respect to the coiling axis.

Spiral lines. Indistinct. Regularly spaced. Approximately 14-24 lines per 1 mm.

Radial ribs running anterior of breathing tube. Radial ribs pronounced, evenly spaced. Approximately 8-15 ribs per 1 mm.

Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 14-21 ribs per 1 mm.

Radial ribs running posterior of breathing tube. Radial ribs unevenly spaced, sometimes distinct but usually absent.

Operculum. Concave, conical. Exterior covered with thin calcareous layer, surface finely granulated. Interior covered with proteinaceous layer, smooth.

Shell colour. Whorls yellow or brownish-red. Peristome white.

Living animal. Body cream-white. Head pink. Tentacles yellow or red.

Habitat and ecology.

Lives on both wet, mossy limestone rock walls and boulders. In shady forests on limestone hills. Some living individuals were observed dangling on mucous threads under rock overhangs.

Distribution range.

Restricted to limestone karsts at central Pahang (Gunung Senyum and Gunung Jebak Puyuh) only.

Differential diagnosis.

Alycaeus senyumensis sp. n. is distinguished from other Alycaeus by its peristome that is distinctly expanded and angled at the columellar section and partially obscuring the umbilicus, narrow ultimate whorl, strong radial ribs, shallow suture and small shell. Alycaeus senyumensis sp. n. is differentiated from the sympatric A. regalis sp. n. and A. costacrassa sp. n. by its much smaller shell and expanded peristome angled at the columellar base.

Discussion.

Historically, Alycaeus senyumensis sp. n. specimens were labelled as A. kelantanensis ( Clements et al. 2008, ZRC collection lots). Alycaeus senyumensis sp. n. occur sympatrically with A. costacrassa sp. n. and A. regalis sp. n. although syntopically only with A. costacrassa sp. n. This is the only Alycaeus species we observed dangling from mucous threads during our fieldwork. Such behaviour in Alycaeus has been recorded in Peninsular Malaysia and Borneo before ( Schilthuizen et al. 1999, Deeleman-Reinhold 2009).