Вероятно, мы нашли категорию простейших по вашему запросу:



Genus Paraquadrula

Shell is transparent, broad oval, slightly compressed laterally; covered by endogenously secreted square or rectangular plates placed in regular rows. Aperture is terminal, slit-like or irregular. Ecology: freshwater, moss and soil. Type species: Paraquadrula irregularis Archer, 1877