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Ectotherms (from the Greek ἐκτός (ektós) "outside" and θερμός (thermós) "hot"), are organisms in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. 

Such organisms (for example snakes or frogs) rely on environmental heat sources, which permit them to operate at very economical metabolic rates. 

 Colloquially, some refer to these organisms as "cold blooded" though such a term is not technically correct, as the blood temperature of the organism varies with ambient environmental temperature. 

Some of these animals live in environments where temperatures are practically constant, as is typical of regions of the abyssal ocean and hence can be regarded as homeothermic ectotherms.

 In contrast, in places where temperature varies so widely as to limit the physiological activities of other kinds of ectotherms, many species habitually seek out external sources of heat or shelter from heat; for example, many reptiles regulate their body temperature by basking in the sun, or seeking shade when necessary in addition to a whole host of other behavioral thermoregulation mechanisms. For home captivity as pet, reptile owners can use a UVB/UVA light system to assist the animals' basking behaviour

Source adapted from: Wikipedia contributors. (2018, June 8). Ectotherm. In Wikipedia, The Free Encyclopedia. Retrieved 02:59, July 16, 2018, from

Frilled Lizard is an example of an ectotherm. Image: R.Conan-Davies