An animal whose body temperature fluctuates with the temperature of its environment is called

The correct answer is a poikilotherm

Explanation:

• Animals are often classified based on their ability to regulate body temperature. This classification determines whether their body temperature remains constant or fluctuates with environmental conditions.
• Poikilotherms are animals whose body temperature varies with the temperature of their surroundings. Unlike homeotherms, they do not maintain a constant internal body temperature. Organisms like amphibians, reptiles, and fish are common examples of poikilotherms as they rely on external heat sources to regulate their body temperature.
• Homoeotherm: These are animals that maintain a constant internal body temperature, regardless of environmental conditions. Examples include mammals and birds. 
• Ectotherm: While ectotherms also rely on external sources of heat for body temperature regulation, this term primarily refers to the source of heat rather than the fluctuation in body temperature.
• Endotherm: These are animals that generate internal heat through metabolic processes to maintain a stable body temperature. Examples include humans, cats, and dogs.