The structure of the carapace and plastron of juvenile turtles, Chelonia mydas (the green turtle) and Caretta caretta (the loggerhead turtle).

Consistent with their primary function as a protective covering, the carapace and plastron are heavily keratinised. In both species, the carapace is heavily pigmented and during the development and translocation of basal cells from the germinal layer of the epidermis, pigment granules migrate towards the surface layers. The epidermis is generally 2-4 cells thick; however at the growing points it can attain 6 cell layers. The epidermis is much thicker over the plastron of the loggerhead turtle. The ultrastructure of the epidermal cells supports the observation that the keratin scales are of the hard variety and the microfolds which characterise the scutes covering the carapace are discussed in relation to the lowering of frictional drag in water.