title: Biogenic calcite granules--are brachiopods different?
abstract: 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 (40-60 nm). 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.
authors.affiliation: Department of Geological Sciences, The University of Alabama, Tuscaloosa, AL 35487, USA. aphuerta@as.ua.edu
authors.forename: Alberto
authors.initials: A
authors.lastname: Pérez-Huerta
authors.forename: Yannicke
authors.initials: Y
authors.lastname: Dauphin
authors.forename: Maggie
authors.initials: M
authors.lastname: Cusack
mesh_terms: D060105:Animal Shells / Q000737:chemistry* / Q000648:ultrastructure; D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry* / Q000378:metabolism; D007448:Invertebrates / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning
chemical_list: D002119:Calcium Carbonate