Mrabella subcarinata (Gauthier-Lièvre 1957) Kosakyan et al., 2016

Description. Shell elongated-pyriform, laterally compressed, with the lateral sides gradually tapering toward the pseudostome. Lateral margins distinctly compressed giving the impression of a thick and wide hollow keel. Because of this, the test is elongated elliptical with the pointed end in the profile. st colourless, composed of quadrangular shell plates similar to those in Quadrulella species. Aperture curved and bordered by a think organic lip.

Dimensions: Shell length 201—218 µm; width 105—127 µm; aperture 35—37.5 µm wide (n = 3).

Differential diagnosis: M. subcarinata is similar to Gibbocarina galeata in general shape of the test and in the presence of a wide, hollow, tuberous keel. Gibbocarina galeata is generally larger, but sizes overlap: L 180—283 µm, W 94—190 µm in G. galeata versus L 201—218 µm; W 105—127 µm in M. subcarinata. As far as known, G. galeata never presents a shell composed entirely of rectangular plates, as is the case in M. subcarinata. M. subcarinata may be confused with M. plicata, which has a similar shape and keel, but it is smaller (L 111—135 µm; W 49—62 µm).