The morphology and lorica development of Phacotus lendneriChodat from waters of the Baltic Lake District (GDR) were studied by light- and by scanning electron microscopy. In “hanging drop” cultures, P. lendneri cells pass through two phases of development: During the first phase lasting 1–3 days, the protoplast grows until it occupies the whole space in the lorica; in the second phase lasting 7 h, the two lorica shells move apart and the protoplast divides into 2, 4 or 8 daughter cells, each of which forms its own lorica. The main component of the lorica is calcite. In the course of lorica formation, the growth and morphology of the calcite crystals differ distinctly from the well-known physico-chemical crystal development phenomena and show clearly that they are determined by the structure of the protoplast surface. The suggestion is put forward as a starting point to explain that lorica calcification in Phacotus lorica is genetically determined and takes place in an organic matrix which, in analogy to the silification structures of diatoms, might be called a “calciolemma”. Further studies will prove this hypothesis. For the first time we succeeded in figuring the primary stages of calcite crystal formation in the “naked” envelope of P. lendneri by SEM techniques.