a, Stained light microscopy section through the scaly carapace integument from a juvenile D. coriacea. Bm, basement membrane; de, dermis; mel, melanophore; stc, stratum corneum; stg, stratum germinativum; and sti, stratum intermedium. b, Autoclave-treated carapace integument from a juvenile D. coriacea showing flattened keratinocytes and melanophores (arrowheads). c, Scaleless carapace integument of an adult D. coriacea revealing multiple layers of stratified squamous keratinocytes. Note the greater thickness of the stratum intermedium in the adult relative to the juvenile individual (compare with a). d, Enlargement of the stratum corneum and stratum intermedium. e, Melanized P. phocoena body integument. B, blubber (dermis and subcutis); epi, epidermis; s, outer skin surface (in oblique aspect). f, Side (top) and internal (bottom) views of artificially compressed P. phocoena integument. g, Light microscopy section through artificially compressed P. phocoena integument showing the condensed blubber layer (compare with e). Er, epidermal ridge. h, Side (top) and internal (bottom) views of P. phocoena integument following autoclave experiments. i, Stained light microscopy section through autoclave-treated integument of P. phocoena. j, Enlargement of the loosely packed superficial blubber (Bs)—a possible entry for microbes (compare Extended Data Fig. 10d)—and dense deeper blubber (Bd). k, Melanosomes in experimentally treated epidermis of P. phocoena. l, m, Shrunken, membrane-bound (arrowheads) adipocytes (or lipid vesicles) in experimentally treated blubber of P. phocoena (compare Extended Data Fig. 10g). n–q, Overlay (n, p) and fluorescent (o, q) images of experimentally treated integument of P. phocoena, exposed to antibodies raised against G. domesticus α-keratin (n, o) and G. domesticus tropomyosin (p, q).