Plectostoma siphonostomum (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 : 34-35

Plectostoma siphonostomum (van Benthem Jutting, 1952) Figure 17N, 23, Appendix 8

Opisthostoma siphonostomum van Benthem Jutting, 1952: 52, figure 27 (original description).

Opisthostoma siphonostomum van Benthem Jutting, van Benthem Jutting (1961: 39).

Opisthostoma siphonostomum van Benthem Jutting, Berry (1964: 203).

Type material.

Holotype: ZMA 136054(1) (Seen). Paratype: ZMA 136055(8) (Seen).

Other examined materials.

ZMA 162138(>100), BOR 5513 (>25), BOR 5521(>10), BOR 5557(>10), V 8199(>50), V 8223(>25).

Diagnosis.

Shares with Plectostoma christae the tuba form, but differs by having an oblong conical apical and conical basal spire.

Description.

Apex. Shape: distinctly convex.

Spire. Height: 1.9-2.1 mm. Width: 1.2-1.5 mm. Number of whorls: 4 3/4-5. Apical spire shape: oblong conical. Basal spire shape: conical. Whorl periphery: distinctly convex. Umbilicus: Open.

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

Tuba. Coiling direction: type 1 and aperture visible between right lateral and back view. Tuba whorl length in proportion to spire last whorl: ca. 3/8-1/2. Proportion of tuba that attaches to spire: at least 1/2.

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: present. Thin lines: present.

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

Distribution.

Type locality. Gua Siput, Taman Negara, Pahang (4°26'47"N, 102°14'44"E).

Distribution range. Plectostoma siphonostomum has a similar distribution pattern as Plectostoma salpidomon and often occurs sympatrically with that species. It can be found in many limestone outcrops in the valley between the Titingwangsa Range, Tahan Range and Benom Range (Figure 18D).

Conservation status.

Least concern. Living populations of Plectostoma siphonostomum were recorded at several limestone hills during surveys between 2010 and 2011. Several of these are located within the National Park.

Discussion.

See discussion under Plectostoma christae .