A tendency for higher maximum life span (MLSP) of cold adapted marine ectotherms was found, when comparing related species with similar lifestyle from permanently cold and temperate waters. We are interested in the physiological principles underlying differences of MLSP in marine ectotherms, especially with respect to the effect of temperature and lifestyle on metabolic rates and reactive oxygen species (ROS) formation. We investigated basic metabolic, antioxidative defence and oxidative damage parameters in different aged individuals of two burrowing mud clams, the Antarctic Laternula elliptica (MLSP ~36years) and the temperate Mya arenaria (MLSP ~ 13years), and two swimming scallops, the Antarctic Adamussium colbecki (MLSP~45years) and the temperate Aequipecten opercularis (MLSP ~ 8-10 years). Of the mud clams, the longer-lived Antarctic species had lower standard metabolic rates and mitochondrial H2O2 generation, resulting in slower decrement of mitochondrial functions and conservation of tissue redox state with age. In the scallop group, a less pronounced decrease in mitochondrial and antioxidant enzyme activities in the Antarctic scallop might account for the higher MLSP. Despite a lower MLSP and the active lifestyle, mitochondria of the temperate scallop exhibit slower senescence than temperate mud clam mitochondria, indicating lifetime energy allocation adjusted to conserve optimal physiological functioning until a threshold is reached where physiological maintenance requires more energy than justified by the reproductive gain.