Plectostoma laidlawi (Sykes, 1902)

Liew, Thor-Seng, Vermeulen, Jaap Jan, Marzuki, Mohammad Effendi bin & Schilthuizen, Menno, 2014, A cybertaxonomic revision of the micro-landsnail genus Plectostoma Adam (Mollusca, Caenogastropoda, Diplommatinidae), from Peninsular Malaysia, Sumatra and Indochina, ZooKeys 393, pp. 1-107 : 71-72

Plectostoma laidlawi (Sykes, 1902) Figures 17O, 48, 49, Appendix 15

Opisthostoma laidlawi Sykes, 1902a: 22 (original description).

Opisthostoma laidlawi Sykes, Sykes (1902b: Plate 3 - figures 13 & 14).

Opisthostoma laidlawi Sykes, von Moellendorff (1902: 143).

Opisthostoma laidlawi Sykes, Laidlaw (1928: 36).

Opisthostoma laidlawi Sykes, van Benthem Jutting (1952: 41).

Opisthostoma laidlawi Sykes, Ito et al. (2009: 58).

Opisthostoma laidlawi Sykes, Sasaki (2010: 126, figure 2.7B).

Type material.

Holotype: Not Seen. Paratype: ZMA 136014(1) (Seen).

Other examined materials.

BMNH C_ACC1825(1), BOR 5510(>25), BOR 5571(2), RMNH 156268(1), ZMA 162095(2), ZMA 162097(>25), ZMA 162099(>10), ZMA 162100(>25), ZMA 162096(1), V5558(1), V 7878(3), V 8345(>100), V 8476(>25), V 8670(>25), V 8693(>50), V 8950(>50), V 9044(>25), V 9109(>25), V 9125(>25), V 9359(6).

Diagnosis.

Shares with Plectostoma annandalei , Plectostoma tenggekensis , and Plectostoma praeco the general shell form in terms of spire and tuba shape, but differs by having a distinctly convex whorl periphery and straight ribs.

Description.

Apex. Shape: moderately to distinctly convex.

Spire. Height: 1.6-2.3 mm. Width: 1.3-1.8 mm. Number of whorls: 3 5/8-4. Apical spire shape: depressed conical. Basal spire shape: conical to ovoid. Whorl periphery: distinctly convex. Umbilicus: open.

Constriction. Parietal teeth: two. Basal teeth: none.

Tuba. Coiling direction: type 2 and aperture visible in right lateral view. Tuba whorl length in proportion to spire last whorl: ca. 5/8-7/8. Proportion of tuba that attaches to spire: varies from completely attached to as much as half of the tuba detached from spire.

Aperture and peristome. Peristome: double peristomes. Outer peristome shape: similar to inner peristome, projected all around, except the posterior part, where the two lateral sides are slightly more projected than the anterior side or left lateral sides slightly more projected than the anterior and right lateral side.

Spiral lines. Thick lines: present. Thin lines: present.

Radial ribs. Rib density: 5-6 ribs per mm. Rib intensity: thin. Shape: straight to slightly curved. Inclination: moderately prosoclin.

Distribution.

Type locality. "Kelantan, Malay Peninsula", collected by J. Waterstradt (Sykes 1902). According to Waterstradt’s (1902) itinerary, he visited one of the limestone hills at Kampung Pulai. The Pulai Princess cave (4°47'38"N, 101°56'31"E) fits perfectly with Waterstradt’s descriptions on the local population, temples and hill’s topography; he also described that he and his collectors sampled shells here ( Waterstradt 1902: 9-10). We conclude that Pulai Princess Cave must be the type locality of Plectostoma laidlawi . However, a recent survey at the highly degraded Bukit Pulai Princess cave failed to retrieve any shells of Plectostoma .

Distribution range. This species occurs on the limestone hills along Berok River and Nenggiri River (Figure 18B).

Conservation status.

Vulnerable (D2 ver. 10.1). Living populations were present on only two limestone hills during a survey in May 2011. All the limestone hills for which this species is known are surrounded by degraded forest and oil palm plantation.

Discussion.

The morphology of this species is quite variable in shell size and degree of attachment of the tuba to the spire. The distribution range partially overlaps with that of Plectostoma davisoni . It is possible that the species actually consists of two or more cryptic species, and thus more genetic data are needed.