exocuticle

The exocuticle is an intermediate layer of the cuticle, which is the outer covering of many invertebrates, particularly arthropods like insects and crustaceans. This tough layer is secreted by the epidermis and is primarily composed of chitin, a strong polysaccharide, embedded in a protein matrix.123

In insects, the exocuticle is sometimes considered the outer part of the endocuticle. The cuticle, including the exocuticle, can be further hardened through a process called sclerotization, where protein chains are stabilized by cross-links, forming sclerotin. This process gives rigidity to structures like body plates and claws. In many crustaceans, the cuticle is also mineralized with calcium salts, making it very hard. The cuticle serves as protection and provides attachment points for muscles. Arthropods must shed their cuticle periodically in a process called molting to grow.14356