Summary:
- Amphibians are vertebrates that exist in two worlds.
- They divide their time between freshwater and terrestrial habitats.
- Amphibians have less variation in size than fish, ranging in length from 1 centimeter (2.5 inches) to 1.5 meters (about 5 feet) Their skin contains keratin, a tough, fibrous protein found in the skin, scales, feathers, hair, and nails of tetrapod vertebrates, from amphibians to humans.
- All amphibians have digestive, excretory, and reproductive systems.