What happens during the stages of crustacean molting?

Crustacean molting is a complex, hormonally regulated process that allows for growth despite the constraints of a rigid exoskeleton. The process is divided into four primary stages:12

• Proecdysis (premolt): The animal prepares for the molt by resorbing calcium from the old exoskeleton into the blood. The epidermis separates from the old shell, new setae form, and a new, soft exoskeleton is secreted beneath the old one.1
• Ecdysis: The actual shedding occurs when the old exoskeleton splits along preformed lines—for example, between the carapace and abdomen in lobsters. The crustacean then withdraws its body from the old shell and immediately swells by rapidly taking in water.132
• Metecdysis (postmolt): The new, flexible cuticle undergoes hardening and calcification as calcium carbonate is deposited into the procuticle.12
• Intermolt: This is the period between molts, which varies in duration. Some crustaceans eventually reach a terminal stage where they no longer molt.1

The process is initiated by the steroid hormone ecdysone, while the timing is influenced by environmental factors and other regulatory hormones.42