Microcystina Moerch , 1872

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 : 27

Taxon classification Animalia Stylommatophora Ariophantidae

Genus Microcystina Moerch, 1872

Nanina subgenus Microcystina Mörch, 1872: 311. Microcystina ( Mörch) Godwin Austen, 1882 (1882-1888): 11.

Diagnosis for the Sabah species.

Shell minute or very small, thin, lenticular, inflated-lenticular to depressed-ovoid; spire almost flat to moderately elevated. Surface shiny or glossy. Sculpture very fine, hardly prominent. Umbilicus open but very narrow, to closed, often partly or entirely covered by a minute, triangular spur protruding from the columellar corner of the peristome; this spur lacking or inconspicuous in juveniles. Dimensions: Width of adult shells 1.7-3.6 mm.

Remarks.

The genus Microcystina includes small (up to 3.6 mm wide) species with lenticular (depressed ovoid in Microcystina physotrochus ) shells. Invariably, the shell surface seems smooth at a first impression, any sculpture present on the shells is very fine and inconspicuous. This distinguishes the smaller species of Microcystina (particularly Microcystina sinica ) from sympatric, yet undescribed Charopa species ( Charopidae ), which have lenticular, minute shells (width of adult shells 0.9-1.9 mm) with a much more conspicuous sculpture. In several Microcystina species the umbilicus is partly or entirely covered by a minute, triangular spur protruding from the columellar corner of the peristome.

Borneo Macrochlamys and Everettia ( Ariophantidae ), and Helicarion ( Helicarionidae ) may have similarly shaped shells, including the inconspicuous sculpture, but they are larger (width of adult shells 8 mm or more).

Placement of Microcystina into the family Ariophantidae follows Schileyko (2003).

We provide a review of the Sabah species of Microcystina . We divide the genus into two informal groups.