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An animal, such as reptiles, fishes, and invertebrates, whose body temperature varies with and is usually higher than the temperature of the environment; a cold-blooded animal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a cold-blooded animal, that is, an animal with a variable body temperature that changes as a function of the temperature of the environment. Poikilotherms include all invertebrates; the only poikilothermic vertebrates are fishes, amphibians, and reptiles.

The body temperature of poikilotherms is generally only 1° or 2° higher than, or equal to, that of the environment. Thermoregulation is imperfect. In many poikilotherms the body temperature rises as a result of muscular work or the absorption of solar heat. For example, the body temperature of bumblebees in flight may reach 38° or even 44°C at an air temperature of 4° to 8°C. However, after the cessation of flight the body cools rapidly to the temperature of the environment. If the external temperature rises above or falls below optimal limits, poikilotherms become torpid or perish. Many of them are in torpor a large part of the year; for example, the turtle Testudo horsfieldi is active only three months of the year. The absence of perfect thermoregulatory mechanisms in poikilotherms may be explained by the relatively poor development of their nervous systems (especially the central nervous system), a level of metabolism approximately 20 to 30 times lower than that of homeo-therms, and other features associated with the fact that poikilotherms have a more primitive organization than birds and mammals.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
In this respect, the frogs resemble Antarctic fishes and numerous other poikilotherms.
Like other poikilotherms, development of PFB is dependent on the ambient temperature, thus completion of pupation period and emergence of adults is likely to vary with the outside temperatures.
Behavioral regulation of body temperature in poikilotherms. Physiologist 13: 399-410.
Gigantism, temperature and metabolic rate in terrestrial poikilotherms. Proceedings of the Royal Society B.
poikilotherms: Animals that are totally dependent upon their environment to regulate body temperature and metabolic activity.
Another source of potential bias in the POF method is the duration of follicular degeneration, which may be temperature-dependent (Hunter and Macewicz, 1985), because the metabolic rates of poikilotherms, like fish, may be directly affected by ambient temperature.
In an insightful review of growth rate variation in plants, homoiotherms, and poikilotherms, Arendt (1997) concludes that high maximum growth rates are selected under conditions of low environmental stress, but this ability trades off with efficient use of resources (or tissue differentiation).
The application of Bergmann's and Allen's rules to the poikilotherms. Journal of Morphology 106: 85-108.
Physiologically based parameters, such as growth, reproduction, distribution, and behavior, of marine poikilotherms are affected by temperature.