Quadrulella deflandrei  Bankov, Todorov and Ganeva, 2021

Diagnosis: Shell large, colorless, ovoid or pyriform in broad view, with sides tapering evenly and gradually from rounded aboral region towards aperture; laterally compressed, with oval transverse section; composed of quadrangular siliceous shell plates of very different sizes, usually mixed and arranged in irregular rows, rarely regularly arranged; aperture oval, slightly convex frontally and concave laterally, bordered by a thin collar of organic cement.

Dimensions: (based on 22 individuals): Length 136–167 μm, width 85–102 μm, thickness 39–45 μm, aperture 33–47 μm.

Ecology: In wet Sphagnum, growing in a small mire in a mixed deciduous forest of beech (Fagus sylvatica L.) and birch (Betula pendula L.), at 881 m a.s.l. in the Western Stara Planina Mts. (Bulgaria).