In marine ectotherms, a trend towards a higher maximum life span (MLSP) is found in polar ectotherms compared to their temperate relatives. Temperature has an impact on metabolic rates and on the intensity of reactive oxygen species (ROS) formation in marine ectothermal species, which, according to the Free Radical-Rate of Living theory (Pearl, 1928; Harman, 1956), could be prime factors responsible for a long MLSP.I investigated chronological and physiological ageing in two burrowing mud clams, the Antarctic Laternula elliptica (Antarctic Peninsula, MLSP~36y) and the temperate Mya arenaria (North Sea, MLSP~13y), and two swimming scallops, the Antarctic Adamussium colbecki (Terra Nova Bay, MLSP~45y) and the temperate Aequipecten opercularis (Irish Sea, MLSP ~8-10y), looking for physiological mechanisms that lead to the different MLSPs.Among the mud clams, the longer-lived Antarctic species displayed higher antioxidant capacities, lower SMR, and reduced rates of mitochondrial H2O2 generation, resulting in a slower decrement of mitochondrial functions and the conservation of tissue redox state with age. In the scallop group, the Antarctic scallop showed a less pronounced decrease in mitochondrial and antioxidant enzyme activities and a lower waste accumulation.Despite a lower MLSP, mitochondria of the active temperate scallop exhibit slower senescence compared to the temperate mud clam, which may indicate a conservation of optimal physiological functioning throughout lifetime in order to evade predation and other interactive extrinsic mortality factors.The results speak for a principle applicability of the Free Radical-Rate of Living theory to the ageing process in marine bivalves, but also indicate, that the absolute values and changes in the investigated parameters are not simply based on environmental temperature regime and lifestyle (mobility), but are also influenced by other interactive parameters within the species specific ecological niche.