Final answer:
Homeotherms, or endotherms, maintain a constant internal body temperature through internal metabolic processes, unlike ectotherms, which rely on external heat sources.
Step-by-step explanation:
The type of animal that maintains a constant internal body temperature is a homeotherm. Homeotherms, also known as endotherms, regulate their body temperature internally through metabolic processes, regardless of external environmental temperatures.
This allows them to maintain high levels of activity even in cooler environments. Mammals and birds are examples of homeotherms. In contrast, ectotherms depend on external heat sources to regulate their body temperature and exhibit varying internal temperatures based on their environment.