Microcystina planiuscula Vermeulen, Liew & Schilthuizen

Vermeulen, Jaap J., Liew, Thor-Seng & Schilthuizen, Menno, 2015, Additions to the knowledge of the land snails of Sabah (Malaysia, Borneo), including 48 new species, ZooKeys 531, pp. 1-139: 37

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scientific name

Microcystina planiuscula Vermeulen, Liew & Schilthuizen

sp. n.

Taxon classification Animalia Stylommatophora Ariophantidae

Microcystina planiuscula Vermeulen, Liew & Schilthuizen  sp. n. Figure 33

Holotype. Malaysia, Sabah, Mt. Trusmadi , Gua Dawaras ( RMNH.5003936). View Materials 

Examined material from Sabah.

Interior Province. Gunung Trusmadi slopes: Gua Loloposon (leg. J.J. Vermeulen, V 13220); Gua Dawaras (leg. M. Schilthuizen, V 12742; leg. M. Schilthuizen, V 9868).


Shell very small, thin, translucent, yellowish brown, discoid-lenticular; spire almost flat. Surface glossy. Whorls moderately convex. Protoconch with 7-10 very fine, widely and regularly spaced spiral grooves. Teleoconch: very fine, widely and sometimes irregularly spaced spiral grooves on the upper and lower surface; these sometimes (partly) absent on the outer whorls. Radial sculpture teleoconch: scattered, inconspicuous growth lines; very slight, irregularly spaced folds just below the suture. Umbilicus open, narrow; columellar side of the peristome somewhat thickened but not covering the umbilicus. Dimensions: Height up to 1.5 mm; width up to 2.6 mm; diameters of the first three whorls 0.7-0.8 mm, 1.2-1.3 mm, c. 2.3 mm respectively; number of whorls up to 3 1/8; height aperture up to 1.2 mm; width aperture up to 1.4 mm.

Habitat in Sabah and distribution.

Primary forest on limestone soil, 1600-1700 m alt. Sabah: Mt. Trusmadi only. Endemic to Sabah.

Cross diagnosis.

Identified by the distinctly more rapidly expanding whorls than in any other species in Group 2.


The name refers to the shell shape [planiusculus (L.) = somewhat flattened].