Marine organisms are affected by the temperature of the water they live in, but they do not necessarily have the same body temperature as the surrounding water. Some marine organisms, such as fish and marine mammals, are able to regulate their body temperature and maintain it at a constant level regardless of the temperature of the water. These animals are known as endotherms or "warm-blooded." Other marine organisms, such as invertebrates and some fish, are not able to regulate their body temperature and their body temperature changes with the temperature of the surrounding water. These animals are known as ectotherms or "cold-blooded."