The animals that rely on the heat from the environment rather than metabolism to raise their body temperature are called
An ectotherm or a poikilotherm is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. Such animals rely on environmental heat sources, such as sunlight or a heated rock surface.
Whereas an endotherm or a homeotherm are organisms that can regulate their body temperature through metabolic activities.