Arthropods possess a rigid exoskeleton, also called cuticle, which they have to replace regularly in order to grow. As a consequence, the life of these animals is closely linked to molting cycles. In most crustaceans, the cuticle is not only hardened by sclerotization, like in hexapods and chelicerates, but by calcification. Thereby, these animals have to find cyclically a source of calcium ions to mineralize each new exoskeleton [1–5]. The origin of the calcium used depends mainly on the way of life of the animal. For aquatic species, postmolt branchial calcium uptake largely contributes to the cuticle calcification, the food being to a lesser extent, another source of calcium ions. Terrestrial crustaceans (among them: amphipods, isopods and decapods), but also some aquatic decapod species, cyclically store calcium in their tissues. Thus, they have a reservoir of calcium ions immediately available after molting for quickly beginning to harden their cuticle in early postmolt. In this case, the complete mineralization of the new cuticle involves remobilization of the stored calcium, branchial uptake and food, the contribution of each source depending of the ecological niche of the animal. The storage
organs, as well as the morphology of the storage structures, are very diverse. For example, terrestrial crabs, lobsters and crayfish store calcium in their stomach wall as one or two pairs of gastroliths