Biomineralizations: insights and prospects from crustaceans

Abstract

For growing, crustaceans have to molt cyclically because of the presence of a rigid exoskeleton. Most of the crustaceans harden their cuticle not only by sclerotization, like all the arthropods, but also by calcification. All the physiology of crustaceans, including the calcification process, is then linked to molting cycles. This means for these animals to find regularly a source of calcium ions quickly available just after ecdysis. The sources of calcium used are diverse, ranging from the environment where the animals live to endogenous calcium deposits cyclically elaborated by some of them. As a result, crustaceans are submitted to an important and energetically demanding calcium turnover throughout their life. The mineralization process occurs by precipitation of calcium carbonate within an organic matrix network of chitin-proteins fibers. Both crystalline and stabilized amorphous polymorphs of calcium carbonate are found in crustacean biominerals. Furthermore, Crustacea is the only phylum of animals able to elaborate and resorb periodically calcified structures. Notably for these two previous reasons, crustaceans are more and more extensively studied and considered as models of choice in the biomineralization research area.

Keywords: ACC; amorphous calcium carbonate; biomineralization; calcification; calcium storage; cuticle; organic matrix.

Figure 1.

Adult specimen of the freshwater red claw crayfish, Cherax quadricarinatus, just after molting (at left the exuviae).

Figure 2.

Calcium storage in the semiterrestrial amphipod, Orchestia cavimana. A Adult male specimen (2-cm long) B Radiography of an adult specimen just after ecdysis (electron-dense stored calcium is well visible in 2 diverticula of the midgut; arrows) C Calcium is stored as calcareous concretions in paired posterior ceca. c: concretion, hg: hindgut, mg: midgut.

Figure 3.

Calcium storage as gastroliths in decapods. A Pair of gastroliths from the crayfish Cherax quadricarinatus (Light Microscopy) B Internal striated structure visible on natural fracture after slight acetic acid decalcification (SEM) C Ultrastructure well visible after natural fracture and high magnification (SEM): the mineral is precipitated as nanospheres D Organic matrix network revealed after acetic acid decalcification (SEM).