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

Taxon classification Animalia Stylommatophora Ariophantidae

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

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

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).

Description.

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.

Etymology.

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