![]() Several interesting theories have addressed the formation of pigmentation patterns. This poor state of knowledge may lead to an incomplete, if not a distorted, view of the mechanisms underlying their morphological evolution. However, despite their importance to many fields, the morphogenetic processes underlying the diversity of shapes remain elusive. Detailed microscopic studies continue to provide important details about the structure and mutual relationships between the mantle, periostracum, and shell. Recent attention has also been given to the formation and differentiation of the shell-secreting mantle margin during development and its morphological variations among classes. Recent studies have begun to identify genes involved in these complex processes and to analyse how they are developmentally regulated, although the physical mechanisms underlying the morphogenesis of the shell ultrastructures remain poorly understood. They have become exemplar model systems for studying the processes of biomineralization, a topic attracting a great deal of interest: from materials science to biomedical applications. Beyond their obvious aesthetic appeal, molluskan shells are an important research area in different fields. The evolutionary success of mollusks, spanning over 540 million years, can be at least partly attributed to the shell that provides both protection and support to the soft body. The huge morphological diversity among classes makes mollusks particularly interesting from an evolutionary perspective, notably with regard to questions related to the origin, evolution, and disparity of their body plan and their shell. With around 200,000 living species, molluska are the second most diversified phylum of the animal kingdom, including gastropods (snails, slugs), bivalves (mussels, oysters,…), cephalopods (squids, Nautilus,…) and five other classes occupying a wide range of marine, freshwater, and terrestrial habitats. ![]() Our main motivation for focusing on generic physical processes involved in development is that they may shape living beings in a predictive way and partly determine the spectrum of forms that have been and could have been generated during evolution. We study the effects of growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and present a “phase diagram” of morphogenesis in molluskan shells. Here we propose a three-dimensional computational framework coupling morphology, incremental surface growth by accretion, and morpho-elastic volume growth, to enable an improved representation of the growth and structural parameters controlling the evolution of these ornamentations. This mechanical basis of “growth and form” has been previously investigated using simplified morpho-mechanical models, but restricted to reduced geometric representations. While the pigmentation patterns are primarily of biochemical origin, the ornamentations result from mechanical deformation of the mantle due to growth induced forces. The distinctive anatomical features of these hard shells are their rich pigmentation patterns and complex structural ornamentations. Molluska are the second most diversified phylum of the animal kingdom, and their evolutionary success can be partly attributed to the hard shell that provides both protection and support to the soft body. Connections are made to a range of complex shells ornamentations. We study the effects of surface and volumetric growth rates, and of previously deposited shell geometries on the resulting modes of mantle deformation, and therefore of the developing shell’s morphology. Calcification of the newest surfaces extends the shell as well as creates a new scaffold that constrains the next growth step. We exercise this framework by applying it to explain the stepwise morphogenesis of seashells during growth: new material surfaces are laid down by accretive growth on the mantle whose form is determined by its morpho-elastic growth. Here, we propose a general, three-dimensional computational framework coupling pre-existing morphology, incremental surface growth by accretion, and morpho-elastic volume growth. The mathematical understanding of the underlying coupling between pre-existing shell morphology, de novo surface deposition and morpho-elastic volume growth is at a nascent stage, primarily limited to reduced geometric representations. Most of the existing literature on the morphology of mollusks is descriptive. During the formation of the shell, the mantle tissue secretes proteins and minerals that calcify to form a new incremental layer of the exoskeleton. Mollusk shells are an ideal model system for understanding the morpho-elastic basis of morphological evolution of invertebrates’ exoskeletons.
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