Plectostoma kakiense (Tomlin, 1948)

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 : 57

Plectostoma kakiense (Tomlin, 1948) Figures 17D, 39, Appendix 11

Opisthostoma kakiense Tomlin, 1948: 225, Plate 2 - figure 5 (original description).

Opisthostoma kakiense Tomlin, van Benthem Jutting (1952: 39).

Opisthostoma kakiense Tomlin, Ali and Yaakob (2001: 145).

Opisthostoma sp., Razalli et al. (2010: figure 2C).

Type material.

Holotype: BMNH 1948.10.2.3(1) (seen).

Other examined materials.

ZMA 136009(1), ZMA 162094(5), BOR 445(1), BOR 5516(>25), BOR 5517(>10), BOR 5598(3), V 8789(2).

Diagnosis.

Shares with Plectostoma kubuensis the general shell form, in terms of apex, spire, and tuba shape, but differs by having two parietal constriction teeth.

Description.

Apex. Shape: slightly to moderately convex.

Spire. Height: 1.7-2.1 mm. Width: 1.5-1.6 mm. Number of whorls: 3 3/4-4 1/4. Apical spire shape: depressed conical. Basal spire shape: ovoid. Whorl periphery: moderately to distinctly convex. Umbilicus: partially closed by tuba.

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. 5/8-3/4. Proportion of tuba that attaches to spire: whole.

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.

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

Radial ribs. Rib density: 8-10 ribs per mm. Rib intensity: thin. Shape: straight to slightly curved. Inclination: moderately prosoclin.

Distribution.

Type locality. Kaki Bukit (6°38'42"N, 100°12'6"E) (Figure 18C). Distribution range. Wang Kelian limestone outcrops.

Conservation status.

Near threatened. To date, only two populations are known for two large limestone outcrops in the vast limestone formation in Perlis. These two locations are Kaki Bukit and Wang Kelian, both located in the protected Wang Kelian State Park.

Although Kaki Bukit is a large limestone outcrop with good forest cover, the population density of Plectostoma kakiense is very low. During a survey in May 2011, this species was only found near the top of Kaki Bukit where several hundred individuals were found at one location (limestone wall) within an area of ca. 10 m2. There were several small populations (fewer than 10 individuals) in small pockets of suitable habitat. The population in Wang Kelian was recorded by Ali and Yaakob (2001), but its status is not known. No live or dead individuals were collected at the dozen isolated limestone hills located within 5 km around Wang Kelian State Park.

Discussion.

See discussion under Plectostoma kubuensis .