 E-C-T-O-T-H-E-R-M, an ectotherm, is an organism in which internal physiological sources of heat are of relatively small or quite negligible importance in controlling body temperature. Such organisms for example 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 its 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 perma-regulation mechanisms. For home captivity as pet, reptile owners can use a UVB slash UVA light system to assist the animal's basking behavior. In contrast to ectotherms, endopherms rely largely, even predominantly, on heat from internal metabolic processes and metatherms use an intermediate strategy. In ectotherms, fluctuating ambient temperatures may affect the body temperature. Such variation in body temperature is called poinkillothermy, though the concept is not widely satisfactory and the use of that term is declining. In small aquatic creatures such as rotifera, the poinkillothermy is practically absolute, but other creatures like crabs have wider physiological options at their disposal, and they can move to preferred temperatures, avoid ambient temperature changes, or moderate their effects. Ectotherms can also display the features of homeothermy, especially within aquatic organisms. Normally their range of ambient environmental temperatures is relatively constant, and there are few in number that attempt to maintain a higher internal temperature due to the high associated costs.