Ecdysis
![Process of ecdysis in the blue crab (Callinectes sapidus)](/Images/godic/202501/10/Callinectes_sapidus4646.jpg")
![Physiology of ecdysis](/Images/godic/202501/10/The-arthropods-moulting-14646.gif")
![After the separation, moulting fluid is secreted into the space between the old cuticle and the epidermis (the exuvial space); this contains inactive enzymes which are activated only after the new epicuticle is secreted.](/Images/godic/202501/10/The-arthropods-moulting-24646.gif")
![The lower regions of the old cuticle are then digested by the enzymes and subsequently absorbed. The process of moulting can start.](/Images/godic/202501/10/The-arthropods-moulting-34646.gif")
Ecdysis is the moulting of the cuticle in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, tardigrades, and Cephalorhyncha. Since the cuticle of these animals typically forms a largely inelastic exoskeleton, it is shed during growth and a new, larger covering is formed. The remnants of the old, empty exoskeleton are called exuviae.