Alycaeus gibbosulus Stoliczka, 1872

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 : 24-27

Alycaeus gibbosulus Stoliczka, 1872 Figures 7 F–G, 17, 31E

Alycaeus gibbosulus Stoliczka, 1872: 268-269, plate 10, figure 14; Pfeiffer 1876: 58; Nevill 1878: 295; Crosse 1879b: 339; Morgan 1885b: 402; Möllendorff 1886: 310; Tenison-Woods 1888: 1068; Kobelt 1902: 344; Sykes 1902: 62; Benthem Jutting 1960a: 13, 19; Davison 1995: 236; Maassen 2001: 21; Clements et al. 2008: 2760; Tarruella and Domènech 2011: 72, figure 1F; Foon et al. 2017: 12, figure 4C.

Alycaeus chaperi Morgan, 1885a: 70.

Alycaeus (Orthalycaeus) gibbosulus : Möllendorff 1891: 342; Kobelt and Möllendorff 1897: 150; Möllendorff 1902: 144.

Alycaeus gibbosulos [sic]: Berry 1963: plate 4.

Dioryx pyramidalis : Habe 1965: 111-112, plate 2, figures 3-4; Maassen 2001: 21. [not Alycaeus pyramidalis Benson, 1856]

Alycaeus (Alycaeus) gibbosulus : Laidlaw 1928: 34; Chan 1998b: 1.

Type locality.

Penang Island.

Type material.

Syntypes. Penang Island: 12 shells deposited at the Indian Museum, Kolkata ( Nevill 1878) (Not seen).

Other examined materials.

Botanic Garden, Penang Island: BOR/MOL 8525/1, BOR/MOL 8526/12. KDH 01 Bukit Baling, Kedah: BOR/MOL 6855/1, BOR/MOL 8358/1, BOR/MOL 8359/23, BOR/MOL 12996/1, ZRC 1975.2.21.182-207/25, ZRC 1975.2.21.144-150/6, ZRC 1997.17/4, ANSP 423057/2. KDH 02 Gunung Pulai, Kedah: BOR/MOL 6857/1, BOR/MOL 8362/16. KDH 10 Bukit Keplu, Kedah: BOR/MOL 6871/1, BOR/MOL 8375/51, BOR/MOL 8376/1, BOR/MOL 6190/1. PRK 62 Gua Dayak, Perak: BOR/MOL 279/1. Mykarst-171 Tasik Temenggor Hill S2, Perak: BOR/MOL 6244/1. PRK 55 Gunung Pondok, Perak: BOR/MOL 6850/1, BOR/MOL 8351/3, BOR/MOL 8352/7, BOR/MOL 11523/1, BOR/MOL 11538/2, ZRC 1972.2.21.140-142/3. Limestone outcrop 50m from roadside, Kampung Pahit, Klian Intan, Perak: BOR/MOL 6875/1, BOR/MOL 8381/3, BOR/MOL 8382/1. Mykarst-027 Gunung Kanthan North, Perak: BOR/MOL 9106/2. Mykarst-025, Perak: BOR/MOL 9382/10, BOR/MOL 9416/2, BOR/MOL 9436/17, BOR/MOL 9500/11. PRK 23 Gunung Rapat, Perak: BOR/MOL 10286/1. PRK 59 Bukit Batu Kurau, Perak: ZRC 1975.2.21.180-181/4. Sungai Siput, Perak: ZRC 1975.2.21.143/1. Capis, upper Perak: ZRC 1975.2.21.1020-1022/3. Gua Kelam, PRS 64 Wang Ulu, Perlis: BOR/MOL 278/1, BOR/MOL 6866/1, BOR/MOL 6868/1, BOR/MOL 8372/4, ZRC 1975.2.21.152-179/27. PRS 19 Bukit Chuping, Perlis: BOR/MOL 6860/3, ZRC 1975.2.21.151/1. Bukit Ayer, PRS 64 Wang Ulu, Perlis: BOR/MOL 6862/1, BOR/MOL 8366/5, BOR/MOL 8367/3, BOR/MOL 12960/1. PRS 17 Gunung Chabang, Perlis: BOR/MOL 6870/1. PRS 40 Bukit Merbok, Perlis: BOR/MOL 8139/1. TRG 01 Bukit Bewah, Terengganu: BOR/MOL 6662/10, BOR/MOL 13002/1. Malakka (= Peninsular Malaysia): RMNH 153521/2.

Description.

Protoconch. Smooth at first whorl, becomes grooved in the second whorl. Grooves arranged parallel to each other and tilted anteriorly at 45° to the coiling axis.

Shell shape. Conical. Shell height: 9.20-10.15 mm. Shell width: 8.46-9.75 mm.

Spire. Spire height: 2.32-3.07 mm. Spire width: 3.32-3.67 mm. Number of whorls: up to 4 ⅛. Spire shape: oblong conical. Whorl periphery rounded. Umbilicus open.

Whorl constriction. At about 4 whorls posterior of protoconch.

Breathing tube. Length: 5.28-6.52 mm.

Aperture and peristome. Aperture circular, moderately expanded. Aperture height: 4.11-5.14 mm. Aperture width: 4.27-4.93 mm. Peristome double, thickened, slightly notched at suture. Interspace narrow to wide. Peristome orientation 18-24° oblique with respect to the coiling axis.

Spiral lines. Indistinct, regularly spaced. Approximately 20-44 lines per 1 mm.

Radial ribs running anterior of breathing tube. Radial ribs pronounced, evenly spaced. Approximately 14-21 ribs per 1 mm.

Radial ribs running perpendicular to breathing tube. Radial ribs more pronounced and thicker than those anterior of breathing tube, evenly spaced. Approximately 8-14 ribs per 1 mm.

Radial ribs running posterior of breathing tube. Ribs absent. Only radial growth lines.

Operculum. Concave, conical. Exterior covered by thick calcareous layer. Exterior has scaffold-like calcareous deposits overlaid on radially spiral lamellae. Interior covered by proteinaceous layer, mamillated.

Shell colour. First 3 whorls usually red, purple or pink. All colours fade to white towards ultimate whorl.

Living animal. Body brown. Head brown. Tentacles light to dark grey.

Habitat and ecology.

Lives under large rotten logs or on leaf litter. In wet, shady forests in both limestone and non-limestone areas.

Distribution.

Widespread from Perlis to Perak on the west coast and in parts of Kelantan and Terengganu on the east coast but not found in Selangor, Pahang and the southern states of Peninsular Malaysia. Elsewhere, in Trang, southern Thailand (as Dioryx pyramidalis (Benson, 1856), in Habe (1965)).

Differential diagnosis.

Alycaeus gibbosulus is most similar to A. conformis in shell shape but differs in having a more expanded penultimate whorl, coarser sculpture, more oblique peristome, longer constriction whorl, longer breathing tube (longer by 0.66 mm), ultimate whorl that is very obtused prior to constriction and scaffold-like calcareous deposits at the operculum exterior. The animal body is brown in A. gibbosulus compared to grey in A. conformis .

Discussion.

The syntypes of A. gibbosulus is housed in the Indian Museum, Kolkata, India ( Nevill 1878) but was not examined in this study. Nevertheless, topotypic specimens from Penang Island (BOR/MOL 8525, BOR/MOL 8526) match the illustration of the type by Stoliczka (1872). This is considered to be sufficient for positive species identification.

This species is closely related to A. conformis and has historically been confused with it. Studies that reported A. gibbosulus in various localities are as follows: Penang ( Stoliczka 1872, Crosse 1879b, Tenison-Woods 1888, Kobelt 1902, Laidlaw 1928, Möllendorff 1891), Perlis ( Benthem Jutting 1960a), Perak ( Crosse 1879b, Möllendorff 1886, Möllendorff 1891, Davison 1995, Chan 1998b) and Kelantan ( Sykes 1902, Möllendorff 1902). Möllendorff (1886) reported that Perak shells differ from Penang shells in being paler as well as possessing a wider ultimate whorl. These shell forms are well within the morphological variation of A. gibbosulus . An erroneous record of Dioryx pyramidalis Benson, 1856 in Peninsular Malaysia has been traced back to a mistake by Habe (1965) in which specimens of A. gibbosulus from northern Malay Peninsula were misidentified as Alycaeus pyramidalis Benson, 1856. The species Alycaeus chaperi Morgan, 1885b, is also a synonym of Alycaeus gibbosulus ( Möllendorff 1886, Möllendorff 1891).

Alycaeus gibbosulus has been reported to exist sympatrically with A. conformis in Gunung Rapat, Perak ( Foon et al. 2017). Elsewhere range overlaps between A. gibbosulus and A. conformis remain unresolved. In Kelantan, Sykes (1902) mentioned a collection of shells with typical A. gibbosulus characters and some which were "much less gibbous". These less gibbous shells are likely A. conformis , which is common in Kelantan. Hence, it is possible that both A. gibbosulus and A. conformis exist sympatrically in Kelantan. In Pahang where only A. conformis records are confirmed, an aberrant record of A. gibbosulus from Kuala Tahan ( Benthem Jutting 1960a) warrants investigation. The shells of A. gibbosulus are sometimes coated in a layer of organic matter when alive (Figure 7F).