The Crustacean Cuticle, Molting, and Seasonal Quality

Another defining characteristic of the crustaceans is a “shell” or cuticle made up of chitin, a network of molecules that are something of a hybrid between carbohydrates and proteins. In shrimp, the cuticle is thin and transparent; in larger animals it’s thick and opaque, hardened to a rock-like mass with calcium minerals filling the space between chitin fibers.

As a crustacean grows, it must periodically cast off the old cuticle and create a larger new one. This process is called molting. The animal constructs a new, flexible cuticle under the old one from its body’s protein and energy reserves. It squeezes its shrunken body through weakened joints in the old shell, then pumps up itself with water—from 50 to 100% of its original weight—to stretch the new cuticle to its maximum volume. It then hardens the new cuticle by cross-linking and mineralizing it, and gradually replaces its body water with muscle and other tissues.