Centropyxis thailandica  Todorov & Golemansky, 1999

Diagnosis: Shell large, brown, a type of plagiostomy with a visor. In ventral and dorsal views it is ovoid. Aperture large, ovoid and sub-terminal. In lateral view a constriction clearly separates the spherical body from a strongly flattened visor. Flattened ventral side is well differentiated. Inner lip of the aperture feebly curved inside, outer lip incurvate forming a strongly flattened visor. Shell surface on the ventral side usually smooth, composed mainly of small siliceous particles, embedded in yellow-brown organic cement. Shell surface on the dorsal side rough, usually composed of bigger quartz particles of various sizes. A few very large quartz particles are visible on the posterior extremity on the dorsal side.

Dimensions: According to Todorov & Golemansky, 1999: Shell length 233-260 µm; width 190-212 µm; height 130-140 µm; diameter of the aperture 110-117 µm.

Habitat: humid epiphytic mosses on tree trunks, height 1-2 m, Thailand, “Khao Yai” National Park.

Remarks: C. thailandica is easily distinguished from the remaining known species of the genus Centropyxis by its biometric characteristics. By its general form this big species resembles only Centropyxis ventricosa Bartos, 1963. C. thailandica differs from the other known species by the larger shell dimensions. Bartos (1963) indicated an average length of 100 µm and an average breadth about 63 µm for C. ventricosa, whereas the same dimensions of C. thailandica were 243 pm and 190 pm, respectively, i.e. almost three times larger. Furthermore, these species are also distinguished from each other by the structure of the visor. The visor of C. ventricosa is composed of two ranges of angular quartz particles and its outer lip is indented, whereas the visor of C. thailandica is composed by many small siliceous particles and its outer lip is not indented (Todorov & Golemansky, 1999).