The crustacean exoskeleton is secreted by the immediately underlying epidermis‑ a single layer of
cuboidal epithelial cells‑ and so it follows that there is exoskeleton above every epidermal layer.
This includes invaginations of the ectoderm and internal structures derived from embryonic
invaginations, such as the foregut and hindgut (often referred to as the endoskeleton).