The integument of lungfish: General structure and keratin composition

The aquatic environment poses less restrictions on mechanical and barrier performances in the integument of both marine and freshwater vertebrates, mainly fish and some amphibians, in comparison to the skin of terrestrial vertebrates (Whitear 1977; Zaccone et al. 2001; Alibardi 2006). As a result, apart from specific locations of the body in a few species of fishes and amphibians, the epidermis of aquatic vertebrates resembles the relatively poorly keratinised multi-layered epithelia found in the mucoses lining the respiratory or alimentary canals of terrestrial vertebrates (Whitear 1986a,b). In particular a corneal layer is missing over the general epidermis of fishes and perennibranchiate amphibians. Th is includes also sarcopterygian fish, both crossopterygians (Latimeria, saltwater) and dipnoans (freshwater). Th is chapter is mainly concerned with the skin, especially the epidermis of the Australian lungfish, Neoceratodus forsteri, which is compared where studies are available, with the epidermis of other species of dipnoans (Kitzan and Sweeny 1968; Imaki and Chavin 1975a,b, 1984). In addition to a previously published study (Alibardi and Joss 2003), N. forsteri skin derived from two extra larval stages are described and the keratins have been partially characterised.