The Class Amphibia includes frogs, toads, salamanders, and caecilians—cold-blooded vertebrates that live both in water and on land during different life stages. Amphibians typically have moist, permeable skin for gas exchange, undergo metamorphosis from aquatic larvae with gills to terrestrial adults with lungs, and lay eggs in water. They are ectothermic, rely on both aquatic and terrestrial habitats, and play important roles as predators of insects and as prey for larger animals, making them key indicators of environmental health.