Amphioxus has an epidermis with a single layer of cells. The horny teeth of lampreys are keratin - most other fishes have little or no keratin in the skin. The earliest tetrapods had dermal scales, which probably functioned as armor. Among living amphibians, caecilians have tiny dermal scales called osteoderms. Their homology with dermal armor is not clear.
Amphibians mark the transition between the aquatic and terrestrial environment.
To prevent water loss, amphibians utilize mucus, which is a similar mechanism that fish use to prevent taking on additional water. However, the mucus in amphibians is secreted by multicellular glands rather than the unicellular glands in fish. Because the integument of amphibians makes them somewhat vulnerable, many amphibians also secrete toxins that prevent them from being eaten by other organisms. The primary gland responsible for the secretion is the parotid gland, located behind the ear of amphibians. Reptiles Reptiles show more advanced integumental adaptations to the terrestrial environment because they are more far-removed from the water.