poikilothermic (ectothermic) Any animal whose body temperature fluctuates with the temperature of its surroundings, often referred to as cold-blooded. Reptiles, amphibians, fish and invertebrates are poililothermic. They can control their body temperature only by their behaviour – by moving in and out of the shade, or orientating themselves to absorb more or less sunlight. See also homeothermic

poikilothermic (poi-kil-oh-therm-ik) adj. cold-blooded: being unable to regulate the body temperature, which fluctuates according to that of the surroundings. Compare homoiothermic.
—poikilothermy n.