Procuticle

Procuticle is the inner portion of the arthropod cuticle, lying beneath the outer epicuticle and secreted by epidermal cells during growth and molting. It is the thick, primarily chitin–protein matrix that forms the main structural component of the exoskeleton, providing mechanical support and a framework for muscle attachment.

The procuticle consists of two sublayers: the exocuticle and the endocuticle. The exocuticle is the outer region of the procuticle and is typically more sclerotized (hardened) through cross-linking of its proteins, contributing to rigidity. The endocuticle is the inner region and is usually less rigid, offering some flexibility while still adding strength. The epicuticle, by contrast, is the very outermost layer and contains waxes and lipids that minimize water loss and provide surface protection.

Formation and development involve secretions from epidermal cells during molting. After apolysis, a new procuticle is deposited, then undergoes sclerotization (tanning) to achieve its final mechanical properties. The procuticle remains attached to underlying epidermis and, after each molt, is renewed as part of the new exoskeleton.

Functionally, the procuticle is critical for protection against physical stress and environmental hazards, serves as a attachment site for muscles, and contributes to the overall rigidity and shape of the animal. Its thickness and degree of sclerotization vary by body region, developmental stage, and species, reflecting different mechanical demands.