Marine and other organisms are classified as homeotherms if they maintain a constant body temperature and as poikilotherms if their body temperature matches that of the environment. A. Although strong-swimming fishes and intertidal organisms have body temperatures that are higher or lower than ambient temperatures, most fishes and subtidal marine organisms are poikilotherms. B. There are no homeotherms in cold ocean waters because it is too difficult for homeotherms to prevent heat loss in these environments. C. Features such as fur help reduce heat loss, but marine homeotherms require a higher metabolism than do terrestrial homeotherms of similar size to maintain a constant body temperature. D. Some organisms are thought to have various methods of heat regulation in order to maintain different body temperatures at different times of year. E. Marine homeotherms lose heat to the environment through respiration and other means, the most important being skin contact with colder seawater. F. Animals with limbs are at a disadvantage regarding body temperature because their circulatory anatomy is poorly designed for managing heat loss.