Amphibians and Reptiles
Amphibians are members of the class Amphibia, whose living forms include frogs, toads, salamanders, newts and caecilians. They are cold-blooded, tetrapod vertebrates. Most have four limbs and live in fresh water or on land but the caecilians, though included in the group, live in burrows in damp soil and are limbless. Amphibians typically have a larval stage that lives in water but there are many different behavioural adaptations that have developed among species to bypass this necessity. The young undergo metamorphosis from a larval form with gills to an adult air-breathing form with lungs. Amphibians also use their skin for respiration and some small terrestrial salamanders rely entirely on this and have no lungs.
Reptiles are members of the class Reptilia comprising the amniotes that are neither birds nor mammals. The amniotes are the vertebrates with eggs featuring an amnion, a double membrane that permits the embryo to breathe effectively on land. Living reptiles can be distinguished from other tetrapods in that they are cold-blooded and bear scutes or scales.
Reptiles are tetrapod vertebrates, either having four limbs or, like snakes, being descended from four-limbed ancestors. Unlike amphibians, reptiles do not have an aquatic larval stage. Most reptiles are oviparous (egg-laying), although certain species of squamates retain the eggs until hatching and a few are viviparous (give birth to live young). As amniotes, reptile eggs are surrounded by membranes for protection and transport that adapt them to reproduction on dry land.
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