Myxostoma petiverianum tenggolensis, Foon, 2016

Foon, Junn Kitt, 2016, Myxostoma petiverianum tenggolensis (Gastropoda: Caenogastropoda: Cyclophoridae), a new subspecies of land snail from Peninsular Malaysia, Raffles Bulletin of Zoology 64, pp. 329-334 : 331-332

Myxostoma petiverianum tenggolensis , new subspecies

( Figs. 1A, E , 3 A–L)

Material examined. Holotype: Shell with operculum (SH 22.9 × SD 32.7 mm) ( MZUM MOG 000001 ), Pulau Tenggol, State of Terengganu, Malaysia (4°48’27.27”N, 103°40’45.60”E), coll. Junn Kitt Foon, 11 April 2008 . Paratypes: 1 shell with operculum (SH 21.9 × SD 33.7 mm) ( MZUM MOG 000002 ), 3 shells (SH 21.7 × SD 31.9 mm, SH 20.6 × SD 30.1 mm, SH 23.4 × SD 32.3 mm) ( MZUM MOG 000003–000005 ), 3 shells (SH 23.9 × SD 32.7 mm, SH 21.0 × SD 30.9 mm, SH 23.4 × SD 32.6 mm) ( BOR / MOL/6220), 2 shells (SH 23.5 × SD 32.3 mm, SH 23.0 × SD 32.7 mm) ( MZK /G/0001–0002), 2 shells (SH 22.7 × SD 32.6 mm, SH 23.5 × SD 32.0 mm) ( ZRC.MOL.6339), same data as holotype .

Comparative material. — Myxostoma petiverianum petiverianum : 1 shell and operculum (SH 24.2 × SD 36.1 mm) ( USNM 316711), Paulo Condor Island [=Con Son Island, Con Đảo Archipelago, Vietnam], coll. Evezard & Henderson, no date; 1 shell and operculum (SH 22.1 × SD 29.0 mm) ( IRSNB p334781), Cochinchine [=southern Vietnam], coll. Germaine de Gottal Anvers, no date.

Description. Shell medium to large sized (SH 20.6–23.9 mm, SD 30.1–33.7 mm [mean SH 22.63± 1.07 mm, SD 32.21± 0.93 mm]), sub-discoidal to sub-globose (spire angle 37°–45°), dome-shaped at aperture view, discoid at dorsal view. Umbilicus wide. Whorls smooth, suture simple and distinct. Fine radial sculpture on all post-apical whorls. Whorls 4.40 when matured. Periphery smooth, rounded. Peristome double, reflexed, thickened and circular; upper part of the peristome developed into a pointed extension along the periphery of the last whorl perpendicular to the coiling axis. Prominent sutural ridge from about 3.5 whorls onwards, with a deep channel running concurrently along the suture interior, terminating at the pointed peristomal extension (indicated with arrow, Fig. 1A ). Shell interior porcellaneous, white. Dorsal side of apical whorls dark purple, occasionally with sparse white or yellow-brown zigzag pattern; dorsal side of post-apical whorls dark brown; umbilical side of apical whorls either purple or brown; umbilical side of post-apical whorls light brown. Peristome colour varies from dark to ochre brown. Periostracum thin, brown, glossy. Without the periostracum, shell base colour is yellow with numerous fine brown radial colour stripes.

Operculum ( Figs. 1E , 3L ): Thick, brown, circular, horny, with a hard nucleus. Interior has strong circular ridge with a depressed centre, a mammilla at the nucleus. Exterior has nine flattened lamellae running anti-clockwise. Periphery is decorated with brown hair-sheets (ciliate) when intact ( Fig. 1E ) but becomes indistinct when eroded ( Fig. 3L ).

Habitat and ecology. Lives on the forest floor of beach and coastal dipterocarp rainforests.

Distribution. Pulau Tenggol, State of Terengganu, Peninsular Malaysia ( Fig. 2 ).

Etymology. This subspecies is named after the type locality Pulau Tenggol.

Remarks. Shell colouration and patterning are distinctively different between Myxostoma petiverianum petiverianum and M. petiverianum tenggolensis . Shells of M. p. petiverianum is characterised by strong white mottled pattern on the dorsal surface and the presence of a dark brown band on the shell periphery. In contrast, shells of M. p. tenggolensis consistently lack peripheral banding and rarely exhibit strong zigzag patterns on the dorsal side of its whorls. In addition, the peristome colour is dark brown to maroon for M. p. petiverianum , while M. p. tenggolensis is dark to ochre brown.

Figures

Fig. 1. Comparison of shells and opercula of Myxostoma petiverianum tenggolensis, new subspecies (A, E), and Myxostoma petiverianum petiverianum (Wood, 1828) (B–D, F–G). Arrows indicate the peristomal extension along the periphery of the last whorl. A, Myxostoma petiverianum tenggolensis, new subspecies, holotype (SH 22.9 × SD 32.7 mm) (MZUM MOG 000001), Pulau Tenggol, Malaysia; B, Myxostoma petiverianum petiverianum (Wood, 1828) (SH 24.2 × SD 36.1 mm) (USNM 316711), Con Son Island, Con Đảo Archipelago, Vietnam; C, Myxostoma petiverianum petiverianum (Wood, 1828) (SH 22.1 × SD 29.0 mm) (IRSNB p334781), southern Vietnam; D, original figure of Cyclostoma petiverianum illustrated in Wood (1828); E, operculum of Myxostoma petiverianum tenggolensis holotype (MZUM MOG 000001); F, operculum of Myxostoma petiverianum petiverianum (Wood, 1828) (USNM 316711); G, eroded operculum of Myxostoma petiverianum petiverianum (Wood, 1828) (IRSNB p334781). Photographs A and E by the author; photographs B and F, courtesy of Robert Hershler (USNM); photographs C and G by Yves Barette, courtesy of Yves Samyn (IRSNB); illustration D from Wood (1828) (no longer in copyright and digitised by the Biodiversity Heritage Library: http://dx.doi.org/10.5962/bhl.title.30661).

Fig. 3. Shells (A–K) and operculum (L) of Myxostoma petiverianum tenggolensis, new subspecies, paratypes from Pulau Tenggol, Malaysia. A, SH 21.9 × SD 33.7 mm (MZUM MOG 000002); B, SH 21.7 × SD 31.9 mm (MZUM MOG 000003); C, SH 20.6 × SD 30.1 mm (MZUM MOG 000004); D, SH 23.4 × SD 32.3 mm (MZUM MOG 000005); E, SH 23.9 × SD 32.7 mm (BOR/MOL/6220); F, SH 21.0 × SD 30.9 mm (BOR/MOL/6220); G, SH 23.4 × SD 32.6 mm (BOR/MOL/6220); H, SH 23.5 × SD 32.3 mm (MZK/G/0001); I, SH 23.0 × SD 32.7 mm (MZK/G/0002); J, SH 22.7 × SD 32.6 mm (ZRC.MOL.6339); K, SH 23.5 × SD 32.0 mm (ZRC.MOL.6339); L, exterior (top) and interior (bottom) view of an eroded operculum (MZUM MOG 000002). All photographs taken by the author.

Fig. 2. Locality records of Myxostoma petiverianum petiverianum (Wood, 1828) (white circles) and Myxostoma petiverianum tenggolensis new subspecies (black circle): 1, Kep National Park, Cambodia (after Egorov, 2016); 2, Con Son Island, Vietnam (after Egorov, 2016); 3, Pulau Tenggol, Peninsular Malaysia (this study).