Biomineralization is the process by which organisms form minerals that they use for support,protection, or nutrient storage, such as shells, skeletons, and bones. It is taxonomically widespreadand biomineralizing species are found among bacteria, algae and several animal groups. Amongthe latter we find corals (class Anthozoa, phylum Cnidaria), drivers of reef formation and accretion.For decades, research on coral biomineralization has mostly focused on scleractinian corals , asthey constitute the main reef building organisms. However, from a bio-mineralogical point ofview scleractinian corals are quite uniform, as they all produce an aragonite exoskeleton. Onthe other hand, their sister taxon, the Octocorallia (commonly known as soft corals) producea high diversity of skeletal structures, until now systematically overlooked in biomineralizationstudies. Significantly, among Octocorals we find species producing aragonite massive skeletons— like their scleractinian relatives — and species with calcitic exo- or endosclerites of differentmorphologies. One of the main questions underlying such biomineral diversity is whether this isdue to independently evolved taxon-specific molecular machineries or rather through a conservedcore set of biomineralization "toolkit" genes that is employed in different ways in different cnidar-ian taxa with lineage specific diversification. Moreover, the effects of abiotic conditions, such asseawater chemistry, on soft corals skeleton characteristics are to date poorly understood. In thelight of the above, we are currently using a multi- disciplinary approach, combining especiallytranscriptomics and proteomics, to comparatively characterize biomineralization molecular toolkitsin octo- and scleractinian corals. Identifying calcification-related genes in these taxa does not onlyprovide an insight into the mechanisms underlying biomineralization in this group, but it alsoallows to investigate the distribution of these genes across Anthozoa and ultimately reconstructtheir evolution and thus the evolution of biomineralization.
