title: Hierarchical architecture of the inner layers of selected extant rhynchonelliform brachiopods.
abstract: In spite of several attempts for a best knowledge of the phylum, brachiopods remain, compared with molluscs, among those least analysed in terms of biomineralization. The lack of economic impact for extant species is probably liable for that situation. Much attention has been on the microstructure of calcite biomaterials (rhynchonelliforms and craniiforms). Here, we emphasize the sub-micrometric structure of selected examples of rhynchonelliform shells using Atomic Force Microscopy (AFM) to complement Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) analyses. The hierarchical organization of the shell layers (secondary and/or tertiary elements) is highlighted for species non-yet observed from this point of view, and is compared to a few already mentioned in the literature. Previous analysis revealed that granules are composed of a complex aggregation of sub-units in intimate relation with an intracrystalline matrix. Their shape, size and probably early orientation depend on the species as well as age and living environments of the specimens studied. The control of the inorganic part of the composite fibrous elements is constrained by the deposition of nearly arched shape or polygonal protein membranes at the inner boundary of the primary layer, prior to the deposition of the first granules, membranes becoming proteinaceous sheathes progressively enshrining fibres. The diverse orientations of the granules in fibrous neighbours thus further increase arguments in favour of the tendency to improve the shell strength.
authors: Muséum National d'Histoire Naturelle, Laboratoire d'Histoire de la Terre, UMR CNRS-MNHN/UPMC 7207 CR2P, 8 Rue Buffon, CP 38, 75005 Paris Cedex, France. Electronic address: ds.gaspard@orange.fr.
authors: Danièle
authors: D
authors: Gaspard
authors: Université Paris Sud - Paris Saclay, UMR-CNRS GEOPS 8148, Bât. 504, Rue du Belvédère, 91405 Orsay, France.
authors: Julius
authors: J
authors: Nouet
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology / Q000648:ultrastructure*; D000818:Animals; D002113:Calcification, Physiologic; D007448:Invertebrates / Q000033:anatomy & histology*; D008566:Membranes; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008974:Mollusca; D011506:Proteins; D013052:Spectrometry, X-Ray Emission
chemical_list: D011506:Proteins
keywords: AFM; Granules; Low-Mg calcite; Rhynchonelliform brachiopods; SEM; SEM-EDX