Biogenic calcite granules—Are brachiopods different?

• Published in: Micron (Oxford, England : 1993) England : 1993), 2013-01, Vol.44, p.395-403
• Main Authors: Pérez-Huerta, Alberto, Dauphin, Yannicke, Cusack, Maggie
• Format: Article
• Language: English
• Subjects: Amorphous calcium carbonate (ACC); Animal Shells - chemistry; Animal Shells - ultrastructure; Animals; atomic force microscopy; biomineralization; Brachiopoda; Calcite; Calcium Carbonate - chemistry; Calcium Carbonate - metabolism; Earth Sciences; Fibers; Granules; Invertebrates - metabolism; Marine; Microscopy, Atomic Force; Microscopy, Electron, Scanning; nanomaterials; scanning electron microscopy; Sciences of the Universe; Semi-nacre
• ISSN: 0968-4328; 1878-4291
• DOI: 10.1016/j.micron.2012.09.005

► SEM and AFM analyses of biomineral structures in brachiopod shells reveal a complex and distinctive style of biomineralization among carbonate-producing organisms. ► Basic carbonate biomineralization mechanisms are not uniform within the Phylum Brachiopoda. ► Calcite fibers of rhynchonelliform brachiopods, mainly within the Order Terebratulida, have large (>100nm), triangular particles that are exceptional among carbonate-producing organisms. ► Proteinaceous envelopes surrounding calcite fibers have a dual function as producers of granules as well as organic templates for the orientation of particles and granules inside mineralized fibers. ► Results may provide independent support for the presence of amorphous calcium carbonate (ACC) in this phylum. Brachiopods are still one of the least studied groups of organisms in terms of biomineralization despite recent studies indicating the presence of highly complex biomineral structures, particularly in taxa with calcitic shells. Here, we analyze the nanostructure of calcite biominerals, fibers and semi-nacre tablets, in brachiopod shells by high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM). We demonstrate that basic mechanisms of carbonate biomineralization are not uniform within the phylum, with semi-nacre tablets composed of spherical aggregates with sub-rounded granules and fibers composed of large, triangular or rod-like particles composed of small sub-rounded granules (40–60nm). Additionally, proteinaceous envelopes surrounding calcite fibers have been shown for the first time to have a dual function: providing a micro-environment in which granules are produced and acting as the organic template for particle orientation as fiber components. In summary, these new findings in brachiopod shells reveal a complex and distinctive style of biomineralization among carbonate-producing organisms.