A layered structure in the organic envelopes of the prismatic layer of the shell of the pearl oyster Pinctada margaritifera (Mollusca, Bivalvia).

The organic interprismatic layers of the mollusc Pinctada margaritifera are studied using a variety of highly spatially-resolved techniques to establish their composition and structure. Our results show that both the interlamellar sheets of the nacre and interprismatic envelopes form layered structures. Additionally, these organic layers are neither homogeneous in composition, nor continuous in their structure. Both structures play a major role in the biomineralization process and act as a boundary between mineral units.