Illumination enhances the protein abundance of sarcoplasmic reticulum Ca-ATPases-like transporter in the ctenidium and whitish inner mantle of the giant clam, Tridacna squamosa, to augment exogenous Ca uptake and shell formation, respectively.

The fluted giant clam, Tridacna squamosa, can perform light-enhanced shell formation, aided by its symbiotic dinoflagellates (Symbiodinium, Cladocopium, Durusdinium), which are able to donate organic nutrients to the host. During light-enhanced shell formation, increased Ca transport from the hemolymph through the shell-facing epithelium of the inner mantle to the extrapallial fluid, where calcification occurs, is necessary. Additionally, there must be increased absorption of exogenous Ca from the surrounding seawater, across the epithelial cells of the ctenidium (gill) into the hemolymph, to supply sufficient Ca for light-enhanced shell formation.