Architecture of crossed-lamellar bivalve shells: the southern giant clam (Tridacna derasa, Röding, 1798)

• Main Authors: O. B. A. Agbaje, R. Wirth, L. F. G. Morales, K. Shirai, M. Kosnik, T. Watanabe, D. E. Jacob
• Format: Article
• Language: English
• Published: The Royal Society 2017-01-01
• Series: Royal Society Open Science
• Subjects: bivalvia; tridacnidae; transmission electron microscopy; electron backscatter diffraction; aragonite; young's modulus
• Online Access: https://royalsocietypublishing.org/doi/pdf/10.1098/rsos.170622

Tridacna derasa shells show a crossed lamellar microstructure consisting of three hierarchical lamellar structural orders. The mineral part is intimately intergrown with 0.9 wt% organics, namely polysaccharides, glycosylated and unglycosylated proteins and lipids, identified by Fourier transform infrared spectrometry. Transmission electron microscopy shows nanometre-sized grains with irregular grain boundaries and abundant voids. Twinning is observed across all spatial scales and results in a spread of the crystal orientation angles. Electron backscatter diffraction analysis shows a strong fibre texture with the [001] axes of aragonite aligned radially to the shell surface. The aragonitic [100] and [010] axes are oriented randomly around [001]. The random orientation of anisotropic crystallographic directions in this plane reduces anisotropy of the Young's modulus and adds to the optimization of mechanical properties of bivalve shells.