Abstract <p>The shell wall ultrastructure is known for three of the four classes of multicameral Foraminifera with a secretive calcareous shell wall: Rotaliata Mikhalevich, 1980; Miliolata Saidova, 1981; and Nodosariata Mikhalevich, 1992. It was believed that one or few large crystals form the wall in Spirillinata Mikhalevich, 1992. The study showed that the entire shell is formed of amorphous, rather than crystalline, CaCO₃ in <i>Raskiniella plana</i> (previously classified as <i>Spirillina plana</i> Wiesner, 1931), which is a typical representative of this class. Amorphous calcareous skeletons are known in certain unicellular algae and multicellular eukaryotes, a skeleton of the entire adult shell completely build of amorphous CaCO₃ was observed for the first time in Foraminifera.</p>