Organization pattern of nacre in Pteriidae (Bivalvia: Mollusca) explained by crystal competition

Abstract

Bivalve nacre is a brick-wall-patterned biocomposite of aragonite platelets surrounded by organic matter. SEM-electron back scatter diffraction analysis of nacre of the bivalve family Pteriidae reveals that early aragonite crystals grow with their c-axes oriented perpendicular to the growth surface but have their a-and b-axes disoriented. With the accumulation of successive lamellae, crystals progressively orient themselves with their b-axes mutually parallel and towards the growth direction. We propose that progressive orientation is a result of competition between nacre crystals at the growth front of lamellae, which favours selection of crystals whose fastest growth axis (b-axis) is oriented parallel to the direction of propagation of the lamella. A theoretical model has been developed, which simulates competition of rhombic plates at the lamellar growth front as well as epitaxial growth of crystals onto those of the preceding lamella. The model predicts that disordered nacre progressively produces bivalve-like oriented nacre. As growth fronts become diffuse (as is the common case in bivalves) it takes longer for nacre to become organized. Formation of microdomains of nacre platelets with different orientations is also reproduced. In conclusion, not only the organic matrix component, but also the mineral phase plays an active role in organizing the final microstructure.

Evidence of a Biological Control over Origin, Growth and End of the Calcite Prisms in the Shells of Pinctada margaritifera (Pelecypod, Pterioidea)

“…Following a purely theoretical approach, Ubukata [32,33] also developed a model of crystallization based on variation of nucleation potential in order to explain the diversity of polygonal patterns within a single shell. Data reported here suggest a challenging view to the "crystal growth competition concept" (CGC) proposed by Checa et al [34,35] as the determinant factor for the morphology of the calcite prisms and other types of microstructures.…”

Evolution of Nacre: Biochemistry and Proteomics of the Shell Organic Matrix of the Cephalopod Nautilus macromphalus

“…[6] It is then surprising to observe that the morphological resemblance between nautilus and abalone nacres is not translated in a "sampling" of their protein contents. This discrepancy is puzzling, in particular because nacre textures are usually considered to be plesiomorphic [19,60] and one should expect their constitutive proteins to be highly conserved during evolution. Our findings suggest, but do not demonstrate, that nacre proteins might be less evolutionarily constrained than expected, and/or that similar types of nacre might be constructed through different biochemical pathways, by use of different "macromolecular tools".…”

The effects of environment on <i>Arctica islandica</i> shell formation and architecture

“…Electron backscatter diffraction (EBSD) has been previously used to determine the crystallographic orientation of gastropod (Fryda et al, 2009;Pérez-Huerta et al, 2011) and bivalve microstructural units (Checa et al, 2006;Frenzel et al, 2012;Karney et al, 2012). Whereas, CRM on mollusk shells is generally applied within studies on taphonomic mineralogical alteration and pigment identification (Stemmer and Nehrke, 2014;Beierlein et al, 2015).…”