Axolotls are aquatic salamanders that primarily breathe through their gills. They do have lungs, but they are not well-developed and are used only in limited situations, such as when the axolotl is out of the water for an extended period. When they are in the water, axolotls rely on their gills to extract oxygen from the water. Because of their aquatic lifestyle, axolotls have evolved to have a flattened body shape with feathery external gills that maximize their surface area for gaseous exchange.