From visible light to X-ray microscopy: major steps in the evolution of developmental models for calcification of invertebrate skeletons

The calcareous skeletons built by invertebrate organisms share a paradoxical property. Although growing outside the mineralizing cell layers the crystal-like skeleton units exhibit morpholo-gies and three-dimensional arrangements that imply an efficient link between crystallization process and taxonomy. Almost two centuries of investigation led to a series of developmental models in which biological and physical or chemical influences are variously balanced. Recent innovative methods allow for their re-examination. From control of the overall shape of the shell to photo-spectroscopic evidence at the atomic level, influence of the biological processes on mineral properties may be a widely shared specificity of the calcareous biomineralization mechanism.