The structural, compositional and mechanical features of the calcite shell of the barnacle Tetraclita rufotincta Liliana Astachov a , Zvi Nevo b , Tamar Brosh c , Razi Vago a,⇑ a Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel b Department of Human Molecular Genetics and Biochemistry, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel c Department of Oral Biology, The Maurice and Gabriela Goldschleger School of Dental Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel article info Article history: Received 4 January 2011 Received in revised form 20 April 2011 Accepted 22 April 2011 Available online 28 April 2011 Keywords: Barnacle Biomineralization Calcite abstract The microstructure and chemical composition of the calcite shell of the sea barnacle Tetraclita rufotincta (Pilsbry, 1916) were investigated using microscopic and analytical methods. The barnacle shell was sep- arated mechanically into its three substructural units: outer, interior, and inner layers. The organic matri- ces of these structural parts were further separated into soluble and insoluble constituents and their characteristic functional groups were studied by FTIR. Investigation of the mechanical properties of the interior mass of the shell reveals remarkable viscoelastic behavior. In general, the mechanical behavior of the shell is a function of its geometry as well as of the material, of which it is constructed. In the case of T. rufotincta, as calcite is a brittle material, the elastic behavior of the shell is apparently related to its micro- and macroarchitecture. The latter enables the shell to fulfill its primary function which is to pro- tect the organism from a hostile environment and enables its survival. Our detailed identification of the similarities and differences between the various structural components of the shell in regard to the com- position and properties of the organic component will hopefully throw light on the role of organic matri- ces in biomineralization processes. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction The barnacle Tetraclita rufotincta (Cirripedia, crustacea) is abun- dant in the western Indian Ocean and off the coast of East Africa (Chan et al., 2009). Barnacles are crustaceans that are permanently cemented to the substrate by a multiprotein complex (Bourget, 1987; Mori et al., 2007). They inhabit shallow and tidal areas, mostly in the sublittoral zone (Doyle et al., 2007), and are highly adapted to a sessile mode of existence. The hard shell that sur- rounds the animal protects it against the physical and mechanical pressures of its habitat and enables it to survive periodic desicca- tion of the tidal zone. According to the official taxonomical hierar- chy used in zoology, the name T. rufotincta, Pilsbry (1916) is the official name of the specie, even though originally Pilsbry had been classified the specie as Tetraclita squamosa rufotincta (T. s. rufo- tincta). However it seems that the status of T. rufotincta is still under discussion and the name T. s. rufotincta sometimes used for the specie (Achituv and Barnes, 1978; Chan et al., 2009; Lowen- stam and Weiner, 1992). Further studies must be conducted on molecular analysis to compare the genetic differentiation, to further ascertains the taxonomic status of the barnacle. Although the barnacle shell has great adaptive significance, few studies have focused on its microstructure. While the general structure and composition of the shell plates of some barnacle species have been investigated (Bourget, 1977; Lowenstam and Weiner; 1992; Rodriguez-Navarro et al., 2006), there has been no detailed study of the relationship between the shell’s architecture and its mechanical properties, and little is known about the organic substances in the shell. Yet it is generally recognized that the or- ganic component is critical for biomineralization processes: it con- trols the formation of crystals of specific morphology and orientation and outlines the design and properties of the shell (Aizenberg et al., 1996; Arias et al., 2004; Bezares et al., 2008; Nudelman et al., 2006). This work focused on the range of substructural elements that have been observed in the shell of T. rufotincta. The crystalline microstructure of the mineralized shell was studied using FTIR, light microscopy and electron microscopy (SEM). Results relating to the organic matrix of the different layers of the shell plates were correlated with their observed structural features. Our analysis of the mechanical and structural properties of the shell shed some light on how a feature such as the shell’s architecture fulfils its mechanical function. It is hoped that the similarities and 1047-8477/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jsb.2011.04.014 ⇑ Corresponding author. Address: Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel. Fax: +972 927 8 6472983. E-mail addresses: eliliana@bgu.ac.il (L. Astachov), rvago@bgu.ac.il (R. Vago). Journal of Structural Biology 175 (2011) 311–318 Contents lists available at ScienceDirect Journal of Structural Biology journal homepage: www.elsevier.com/locate/yjsbi