Describing animals whose body temperature varies with environmental temperature, typically synonymous with ectothermic. Their body temperature fluctuates rather than remaining constant.
From Greek 'poikilos' meaning varied or changeable and 'thermos' meaning heat, literally 'variable heat.' The term emphasizes the changing nature of body temperature in these animals, contrasting with homeothermic species.
Some poikilothermic animals like certain fish can actually switch between being ectothermic and endothermic depending on activity level! Tuna and some sharks can warm their swimming muscles while keeping the rest of their body at ambient temperature.
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