Plectostoma turriforme (van Benthem Jutting, 1952)

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 : 45-47

Plectostoma turriforme (van Benthem Jutting, 1952) Figure 31, Appendix 8

Opisthostoma turriforme van Benthem Jutting, 1952: 43, figure 22 (original description).

Type material.

Holotype: ZMA 136068(1) (Seen). Paratypes: ZMA 136069(>10) (Seen).

Other examined materials.

BOR 461(2), BOR 5609(2).

Diagnosis.

Shares with Plectostoma sciaphilum and Plectostoma senex the tuba form, but differs by having two lamella-shaped constriction teeth and having more than 6 whorls.

Description.

Apex. Shape: distinctly convex.

Spire. Height: 3.2 mm. Width: 1.6 mm. Number of whorls: 7. Apical spire shape: oblong conical. Basal spire shape: conical. Whorl periphery: distinctly convex. Umbilicus: completely closed by tuba.

Constriction. Parietal teeth: two. Basal teeth: two.

Tuba. Coiling direction: type 3 and aperture visible in left lateral view. Tuba whorl length in proportion to spire last whorl: ca. 3/8. Proportion of tuba that attaches to spire: whole.

Aperture and peristome. Peristome: double peristomes. Outer peristome shape: same as inner peristome and uniformly projected all around, except the posterior part.

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

Radial ribs. Rib density: 5 ribs per mm. Rib intensity: thin. Shape: slightly curved. Inclination: orthoclin.

Distribution.

Type locality. Bukit Tenggek, Pahang (4°0'51"N, 103°9'34"E).

Distribution range. In addition to the type locality, this species can be found at nearby Bukit Sagu (Figure 18A).

Conservation status.

Critically Endangered (B2ab(iii)+C2a(i) ver. 10.1). The whole Bukit Tenggek will disappear by 2014 because of quarrying activity. Moreover, more than half of Bukit Sagu has already been quarried away (see also Schilthuizen and Clements 2008). Although living individuals had been recorded from Bukit Sagu in 1997 (BOR 5609), neither living nor recently dead individuals were found in a recent survey conducted in 2010 and 2011.

Discussion.

Plectostoma turriforme , Plectostoma sciaphilum , and Plectostoma senex are three very similar species than occur in the four lenticular easternmost limestone hills in Peninsular Malaysia (Figure 18A). These four hills, namely, Bukit Panching, Bukit Charas, Bukit Sagu, and Bukit Tenggek are located along a 15 km longitudinal transect. Plectostoma turriforme occurs at the two former sites and Plectostoma senex at the two latter sites. Plectostoma sciaphilum occurs sympatrically with Plectostoma turriforme in Bukit Panching. These four hills (and thus the three species) are among the most isolated limestone outcrops in Peninsular Malaysia.