Plectostoma palinhelix (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 : 47-48

Plectostoma palinhelix (van Benthem Jutting, 1952) Figures 17C, 32, Appendix 12

Opisthostoma palinhelix van Benthem Jutting, 1952: 40, figure 20 (original description).

Type material.

Holotype: ZMA 136030(1) (Seen). Paratype: ZMA 136031(>10) (Seen).

Other examined materials.

BOR 466(1), BOR 5520(5), V 5104(5).

Diagnosis.

Shares with Plectostoma retrovertens the spire and tuba form, but differs by having spire height between 1.6-1.9 mm.

Description.

Apex. Shape: slightly convex.

Spire. Height: 1.6-1.9 mm. Width: 1.1-1.3 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 or completely closed by tuba.

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

Tuba. Coiling direction: type 2 and aperture visible between right lateral and back view; the tuba coils upward until the first teleconch whorl of the spire. Tuba whorl length similar to that of the last whorl of the spire. Proportion of tuba that attaches to spire: whole.

Aperture and peristome. Peristome: double peristomes. Outer peristome shape: similer 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: present. Thin lines: present.

Radial ribs. Rib density: 7-8 ribs per mm. Rib intensity: thin. Shape: straight. Inclination: orthoclin.

Distribution.

Type locality. Bukit Serdam, Pahang (3°49'47"N, 101°55'36"E).

Distribution range. To date, this species has been recorded from three limestone hills, namely Bukit Serdam, Gua Kechil and a small hill nearby (Figure 18C).

Conservation status.

Vulnerable (B2ab(iii) ver. 10.1). There are four limestone hills in this area, of which Bukit Serdam and its next unnamed hill support populations (assessment done in 2010 and 2011). Two of the hills, namely, Bukit Serdam and Gunung Panas, are now being quarried. The smallest unnamed hill is highly degraded and Gua Kechil is surrounded by oil palm plantation.

Discussion.

See discussion under Plectostoma retrovertens .