Orientation of Apatite and the Organic Matrix in Lingula Shells

Abstract

Lingula (Brachiopoda, Inarticulata) is a primitive animal which developed some 500 million years ago [1]. The shell is composed of alternating mineralized and the organic layers. The shell is unique, since apatite crystals grow in the organic matrix with a preferred orientation forming alternations of mineralized and the organic layers. CaCO3 crystals grow into various morphology depending on the organic matrix in molluscan shells. Roles of the organic matrix on the regulation of the oriented and uniform growth of CaCO3 crystals have been studied extensively [2–8]. In the case of Lingula shells, the mechanism of orientation of apatite crystals is still unclear. To clarify the mechanism, the structural relationship between apatite crystals and the organic matrix and the differences in the organic component between the mineralized and the organic layers are investigated.