Alycaeus costacrassa, 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 : 20-22

Alycaeus costacrassa sp. n. Figures 7M, 15, 31N

Alycaeus perakensis var. minor nomen nudum, Clements et al. 2008: 2760.

Type locality.

Mykarst-065 Batu Balong, Pahang (3°42'41"N, 101°51'25"E).

Type material.

Holotype. Mykarst-065 Batu Balong, Pahang: BOR/MOL 12995. Paratypes. Mykarst-065 Batu Balong, Pahang: BOR/MOL 8320/2, BOR/MOL 6811/4, BOR/MOL 8319/6.

Other examined materials.

KTN 06 Gua Ikan, Kelantan: BOR/MOL 6631/1. KTN 148 unnamed hill, Kelantan: BOR/MOL 12993/1. KTN 95 Gua Panjang, Kelantan: BOR/MOL 12994/12. PHG 15 Gua Bama, Pahang: BOR/MOL 243/1, BOR/MOL 6235/4, BOR/MOL 6818/2, BOR/MOL 8323/2, BOR/MOL 8324/6. Mykarst-169 Gua Gajah, Pahang: BOR/MOL 6250/5, BOR/MOL 12992/1. PHG 03 Gunung Jebak Puyuh, Pahang: BOR/MOL 6628/3, BOR/MOL 6882/1. PHG 05 Bukit Cintamanis, Pahang: BOR/MOL 6634/2, BOR/MOL 6892/2. PHG 01 Kota Gelanggi, Pahang: BOR/MOL 6635/1, ZRC 1975.2.24.356-372/7, ZRC 1975.2.24.373-402/30. PHG 16 Gua Sai, Pahang: BOR/MOL 6637/80, BOR/MOL 6638/30, ZRC 1975.2.21.557-564/10. Ulu Keniyam Kechil, Pahang: ZRC 1975.2.22.660-692/32.

Etymology.

In Latin - costa crassa, meaning thick ribbed. Named after the species’ diagnostic widely spaced, pronounced radial ribbing of the whorls.

Description.

Protoconch. Smooth.

Shell shape. Conical. Shell height: 3.47-6.37 mm. Shell width: 3.42-6.12 mm.

Spire. Spire height: 1.06-2.43 mm. Spire width: 1.53-2.79 mm. Number of whorls: up to 5 ¼. Spire shape: oblong conical. Whorl periphery rounded. Umbilicus open.

Whorl constriction. At about 5 whorls posterior of protoconch.

Breathing tube. Length: 0.30-0.67 mm.

Aperture and peristome. Aperture circular, moderately expanded. Aperture height: 1.79-2.89 mm. Aperture width: 1.62-2.84 mm. Peristome double, not thickened, winged at suture. Peristome orientation 26-39° oblique with respect to the coiling axis.

Spiral lines. Distinct. Regularly spaced. Approximately 19-52 lines per 1 mm.

Radial ribs running anterior of breathing tube. Radial ribs pronounced, evenly spaced. Approximately 9-18 ribs per 1 mm.

Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, evenly spaced. Approximately 11-17 ribs per 1 mm.

Radial ribs running posterior of breathing tube. Radial ribs pronounced and ueneven immediately posterior of constriction, becoming pronounced and evenly spaced towards the aperture. Approximately 10-21 ribs per 1 mm.

Operculum. Concave, rounded. Exterior covered with thick but flaky calcareous layer, surface finely granulated. Interior proteinaceous layered, smooth, with indistinct mamilla.

Shell colour. Whorls yellow, fading to white posterior of constriction. Peristome white.

Living animal. Body cream-white. Head pinkish brown. Tentacles reddish-brown.

Habitat and ecology.

Lives on wet limestone walls covered with mosses. Occassionally found in crevices, on lower parts of tree trunks. In shady forests on limestone hills.

Distribution range.

Widespread from southern Kelantan to central Pahang.

Differential diagnosis.

Alycaeus costacrassa sp. n. most resembles A. selangoriensis sp. n. in its thick operculum, pronounced radial ribbing and spiral lines but has a narrower ultimate whorl and a more circular peristome without posterior folding at the upper palatal section. Alycaeus costacrassa sp. n. also resembles A. kapayanensis in shell shape but differs in its consistently more pronounced radial ribs as well as operculum with thicker calcareous exterior.

Discussion.

Shells of A. costacrassa sp. n. are consistent in their diagnostic characters but vary considerably in shell size and whorl convexity across its range. Populations in Gua Sai and Gua Bama have the smallest shells (Shell height: 3.47-4.46 mm, Shell width: 3.42-4.27 mm, Figure 15 M–Q) with less rounded whorls. Gua Gajah shells are intermediate in size (Shell height: 4.85 mm, Shell width: 4.67 mm, Figure 15 R–V) with rounded whorls. Batu Balong and Gua Panjang have larger shells (Shell height: 4.99-5.94 mm, Shell width: 4.66-5.58 mm, Figure 15 A–E) with rounded whorls. It is possible that A. costacrassa sp. n. may contain several cryptic species pending availability of molecular data for investigation.