Cuticle Structure

diagram of cuticle layers

The cuticle is secreted by the epidermis, a continuous layer of living cells, which is supported on a non-cellular basement membrane. This membrane separates the exoskeleton from the haemocoel (main body cavity). Immediately above the epidermis is the procuticle, a hydrophilic layer comprised of chitin microfibers within a protein matrix. When the procuticle forms, it is laid down in thin layers and in each layer the chitin microfibers are laid down at a slightly different angle. The procuticle differentiates into a soft, pale inner layer (endoculticle) and a hard, darker layer (exocuticle).

Above the procuticle lies the epicuticle, the outer layer of the cuticle. The epicuticle is comprised of three layers: the basal layer is the cuticulin layer, a complex of lipoproteins and fatty acid chains, followed by a monolayer of wax molecules, which is in turn overlaid by a protective cement layer.