Cuticle

The nonliving external layer secreted by arthropods that forms much of their exoskeleton. It combines structural proteins with chitin and may be hardened or chemically modified.

Chitin: A structural polysaccharide found in arthropod cuticles and fungal cell walls. Chitin fibers reinforce the cuticle's protein matrix.
Arthropoda: The animal phylum of invertebrates with jointed appendages and segmented bodies. Arthropods are the animals whose cuticle defines this external covering.
Insect wings: Paired appendages of insects, supported by veins and formed from cuticular sheets. Their thin cuticle combines lightness with stiffness for flight.
Vertebrate skin: The living, multilayered external tissue covering vertebrate bodies. Unlike arthropod cuticle, vertebrate skin is living tissue and grows with the body.
Arthropod cuticle layers: The epicuticle, procuticle, and associated subdivisions that make up an arthropod's external covering. These layers divide waterproofing, structural support, and growth-related functions.
Exoskeleton: A supportive structure on an animal's exterior rather than inside its body. The cuticle forms much of the arthropod exoskeleton.
Arthropod joint: A flexible connection between hardened regions of an arthropod exoskeleton. Flexible cuticle lets rigid plates move relative to one another.
Mollusk shell: A hard protective structure secreted by the mantle of many mollusks, often rich in calcium carbonate. It is another secreted external armor, but its mineralized composition differs from cuticle.
Sclerotization: Chemical cross-linking that hardens arthropod cuticle proteins after secretion. It stiffens cuticle in body regions that need durable support.
Epidermis (arthropods): The living cell layer beneath an arthropod's cuticle that secretes and renews it. Cuticle is produced by the epidermis rather than being living tissue itself.

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