Difficult to tell at first, because tortoises and terrapins are both slow-moving armored reptiles. Tortoises live on dry land in many warm parts of the world. They usually have high-domed shells, and feed mainly on plants. Terrapins live in fresh water. They have flattened shells, which make them more streamlined as they swim. They often have partly webbed feet and they feed on fish and other animals. Some terrapins are quite large, fierce predators.