Plectostoma davisoni, Liew, Thor-Seng, Vermeulen, Jaap Jan, Marzuki, Mohammad Effendi bin & Schilthuizen, Menno, 2014

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 : 54-55

Plectostoma davisoni sp. n. Figure 37, Appendix 9, 10

Type material.

Holotype: BOR 5646(1)

Paratypes: ZMA 162069(>25), ZMA 162070(3), ZMA 162071(>50), ZMA 162146(7), ZMA 162147(8), BOR 5508(>25), BOR 5626(>25), BOR 5641(9), V 8652(6), V 8929(>25), V 9206(6), V 8265(>10), V 8301(>25), V 9243(>50), V 9340(7), V 9417(7), V 14242(5).

Diagnosis.

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

Etymology.

This species is named after Dr. Geoffrey Davison, who has been involved in the conservation of limestone hills in Malaysia, and has collected a lot of snail specimens, many of which are included in this revision of Plectostoma from Malaysia.

Description.

Apex. Shape: slightly to moderately convex.

Spire. Height: 1.6-2.0 mm. Width: 1.4-1.5 mm. Number of whorls: 3 5/8-4 7/8. Apical spire shape: depressed conical. Basal spire shape: ovoid. Whorl periphery: moderately to distinctly convex. Umbilicus: open.

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

Tuba. Coiling direction: type 2 and aperture visible in frontal 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: 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: 6-7 ribs per mm. Rib intensity: thin. Shape: straight. Inclination: orthoclin.

Distribution.

Type locality. Limestone hill on the right hand side of the road D29, at km 17 when travelling from Jelawang to Gua Musang (4°59'4"N, 101°57'53"E).

Distribution range. This species has a very large distribution range, ca. 80 km diameter. It can be found in many limestone outcrops in the central part of Peninsular Malaysia, mainly in the State of Kelantan (Figure 17D). In addition, it can also be found in a cluster of limestone hills located at upper Sungai Keniyam Kecil in Taman Negara (ca. 60 km from Gua Musang).

Conservation status.

Least concern. This is a widespread species. Although many hills in Kelantan are being degraded and surrounded by oil palm plantations, there are a few well protected hills in Taman Negara in Pahang, where this species occurs.

Discussion.

This species is highly variable in the shell form (Appendix 9 and Appendix 10), and has a very wide distribution range which partly overlaps with many other Plectostoma species (Figure 18). It is very densely distributed in the State of Kelantan, parapatric with Plectostoma christae . The species becomes more sparse toward the limestone hills in Taman Negara, Pahang (Figure 18C). In view of this, it is possible that the species actually consists of two or more cryptic species, and thus more genetic data are needed.