Plectostoma laemodes (van Benthem Jutting, 1961)

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 : 59-60

Plectostoma laemodes (van Benthem Jutting, 1961) Figure 41, Appendix 12

Opisthostoma laemodes van Benthem Jutting, 1961: 40, plate 11 - figure 6 (original description).

Type material.

Holotype: ZMA 136010(1) (Seen). Paratypes: ZMA 136011(3) (Seen), ZMA 136012(3) (Seen), ZMA 136013(4) (Seen).

Other examined materials.

RMNH 156267(7), V 8490(>25).

Diagnosis.

Shares with Plectostoma salpidomon the general shell form, in terms of apex, spire, and tuba shape, but differs by having the whole tuba attached to the spire.

Description.

Apex. Shape: distinctly convex.

Spire. Height: 2.3-2.7 mm. Width: 1.6-1.8 mm. Number of whorls: 3 1/8-4 5/8. Apical spire shape: depressed conical. Basal spire shape: ovoid. Whorl periphery: moderately to distinctly convex. Umbilicus: open or partially closed by tuba.

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

Tuba. Coiling direction: type 3 and aperture visible in right lateral view. Tuba whorl length in proportion to spire last whorl: ca. 1/2-5/8. 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 left lateral sides are slightly more projected than the anterior and right lateral side.

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

Radial ribs. Rib density: 6-7 ribs per mm. Rib intensity: thin. Shape: straight to slightly curved. Inclination: prosoclin.

Distribution.

Type locality. Batu Tai Gadjah, Ulu Keniyam Kechil, Taman Negara, Pahang Malaysia (4°37'0"N, 102°25'14"E) (Figure 18B).

Distribution range. This species mainly occurs in a cluster of limestone hills that are located at upper Sungai Keniyam Kecil in Taman Negara (Figure 18B). In addition, this species has been recorded from Bukit Jereng, Blau, Kelantan, which is about 80 km west from Sungai Keniyam Kecil.

Conservation status.

Least concern. Although no living population has been recorded so far, several large and well protected limestone hills in the Taman Negara probably support a viable population.

Discussion.

From a conchological point of view, this species is similar to Plectostoma salpidomon ; the two may be closely related. In view of biogeography, this species occurs parapatrically with Plectostoma salpidomon , which occurs in the limestone hills in between Bukit Jereng and the limestone cluster at Sungai Keniyam Kecil (Figure 18B). Further genetic data are needed to verify the taxonomic status of Plectostoma laemodes .