The Biology and Evolution of Calcite and Aragonite Mineralization in Octocorallia

Octocorallia (class Anthozoa, phylum Cnidaria) is a group of calcifying corals displaying wide diversity mineral skeletons. This includes skeletal structures composed different calcium carbonate polymorphs (aragonite and calcite). represents unique feature among anthozoans, as scleractinian (subclass Hexacorallia), main reef builders focus biomineralization research, are all characterized by an aragonite exoskeleton. From evolutionary perspective, the presence aragonitic skeletons in puzzling it observed very few species has apparently originated during Calcite sea (i.e., time interval calcite-inducing seawater conditions). Despite this, octocorals have been systematically overlooked studies. Here we review what known about octocoral biomineralization, focusing on biological processes that underlie calcite formation. Although differences research between scleractinians often mentioned, highlight how strong variability also exists groups. Different aspects fact studied small set species, including (calcitic) gorgonian Leptogorgia virgulata and/or precious coral Corallium rubrum. These include descriptions cells (scleroblasts), transport chemistry calcification fluids. With exception histological observations, no information these features available for octocorals. Availability sequencing data heterogeneous groups, with transcriptome or genome available, instance, clade Calcaxonia. far most common polymorph deposited octocorals, argue studying aragonite-forming could provide insight octocoral, more generally anthozoan, biomineralization. First foremost would allow to compare highlighting homologies differences. Secondly, similarities (exoskeleton) Heliopora skeletons, further which driven skeleton characteristics (shared octocorals) those taxonomy regardless polymorph). Including anthozoan mineralization strategies into studies remains thus essential comprehensively study form evolved within this ecologically important marine animals.