Amphibian skin is moist and scaleless. Even those species with lungs (and most adult amphibians have them) breathe at least partly through their skin. They can also lose water through that permeable cloak, so most species are closely tied to wet environments. The skin of reptiles, by contrast, is scaled, and they respire with lungs upon birth.
Reptiles are born either from hard-shelled eggs (laid on land) or directly from their mother's body. While they will grow substantially in size, their basic form mirrors that of the adults. Most amphibians hatch from shell-less eggs laid and fertilized underwater, and transform from aquatic, gill-breathing larvae to adults that breathe air and are capable of terrestrial life.
Amphibians and most reptiles have three-chambered hearts: two atria and one ventricle. Crocodilians have a divided ventricle, making their hearts essentially four-chambered (like those of birds and mammals, which are otherwise quite different).
Amphibians lack claws on their toes; those of reptiles, when they exist, are clawed.
Because reptiles are not as tied to water as moist-skinned amphibians, they can inhabit a greater diversity of habitats, including very arid regions. (However, amphibians are immensely adaptable; there are many, like the Sonoran desert toad, that persist even in deserts by going underground and taking advantage of scattered water resources.)
