Plectostoma klongsangensis (Panha, 1997)

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 : 63-64

Plectostoma klongsangensis (Panha, 1997)

Opisthostoma klongsangensis Panha, 1997: 133, figure 1 (original description).

Opisthostoma klongsangensis Panha, Hemmen and Hemmen (2001: 39).

Opisthostoma klongsangensis Panha, Nabhitabhata (2009: 50).

Type material.

Holotype: CUIZMD 0001 (not seen). Paratypes: CUIZMDM 0002 (Not seen), CUIZMDM 0003 in ZMA (Not seen, specimen could not be located in ZMA).

Diagnosis.

Shares with Plectostoma charasense , Plectostoma tohchinyawi , and Plectostoma kitteli the general shell form, in terms of apex, spire, and tuba, but differs by having both thin and thick spiral lines, and the left lateral side of outer peristome projected more than three times the distance of the right lateral side of outer peristome.

Description (estimated from figure in Panha 1996). Apex. Shape: distinctly convex.

Spire. Height: 2.3 mm. Width: 1.7 mm. Number of whorls: 5 1/2. Apical spire shape: oblong conical. Basal spire shape: conical. Whorl periphery: distinctly convex. Umbilicus: open.

Constriction. Unknown.

Tuba. Coiling direction: type 2 and aperture visible in right lateral view. Tuba whorl length in proportion to spire last whorl: ca. 7/8. Proportion of tuba that attaches to spire: less than 2/3.

Aperture and peristome. Peristome: double peristomes. Outer peristome shape: different from inner peristome, the left lateral side of outer peristome is projected from inner peristome about 0.7 mm, and the right side of outer peristome about 0.1 mm, but narrowed toward the anterior part of outer peristome.

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

Radial ribs. Rib density: 3 ribs per mm. Rib intensity: thick. Shape: single-looped. Inclination: prosoclin.

Distribution.

Type locality. Khlong Saeng Wildlife Sanctuary Surat Thani Province, Thailand (8°31'13"N, 98°25'17"E) (Figure 18B).

Distribution range. Unknown.

Conservation status.

Data deficient. This species has been collected once in Khlong Saeng Wildlife Sanctuary.

Discussion.

From a conchological point of view, this species appears not to be related to Plectostoma species from the Malay Peninsula and Sumatra. Instead, it is almost identical to Plectostoma mirabile , an endemic species from Gomantong Cave, Sabah, Borneo. These two species are separated by the South China Sea and located more than 2000 km apart. It remains to be determined whether this similarity is due to a disjunct distribution of closely related forms, or rather convergent shell evolution.

The taxonomic status of the species remains doubtful. In the original publication, Panha (1996) compared it with Plectostoma heteropleuron ( Vermeulen 1994) and Plectostoma perspectivum (Vermeulen, 1994) from Northern Borneo, but not with Plectostoma mirabile (Smith, 1893), which has an almost identical shell as Plectostoma klongsangensis . This is all the more remarkable, as Plectostoma mirabile (Smith, 1893) was treated in Vermeulen (1994), where both Plectostoma heteropleuron and Plectostoma perspectivum were originally described.

In conclusion, more data are needed to verify the taxonomic status and the interesting biogeography of this species.