Quantitative Micro-CT Characterization of Shell Mineralization Patterns and Structural Adaptations in Molluscan Classes

Marine molluscs serve as essential ecosystem engineers, with their shells functioning as vital geochemical records of historical and current environmental conditions, in addition to providing structural protection. Four key parameters of shell biomineralization, shell mineral density (SMD), porosity, microstructural layer thickness (MLT), and calcified shell volume (CSV) were quantitatively evaluated in this study using high-resolution micro-computed tomography (Micro-CT) across four major shelled classes of Mollusca (Polyplacophora, Gastropoda, Bivalvia, and Cephalopoda) covering three ontogenetic stages (juvenile, subadult, and adult) and three anatomical regions (R1, R2, R3) to elucidate phylogenetic and developmental trends in shell architecture. Analysis reveals that Polyplacophora showed the highest SMD and the lowest porosity percentages, reflecting the evolution of extremely compact and mechanically resistant armour tailored for survival in high-energy intertidal habitats. Over their ontogeny, gastropods displayed increased mineral enrichment and thickness, indicating sustained structural reinforcement. Bivalvia exhibited ontogenetic modulation of calcified shell volume corresponding to progressive hinge specialization, while cephalopods showed heterogeneous mineral density corresponding to buoyancy control mechanisms. SMD and porosity displayed an inverse association across all molluscan classes, demonstrating a preserved biomineralization pattern. This study advances understanding of marine invertebrate shell development and adaptive design by establishing a quantitative, non-destructive, three-dimensional framework.