The ocean quahog Arctica islandica is one of the longest-living and slowest-growing marine bivalves. The oldest specimens obtained for the present study approached 200 yr. To achieve such a long lifespan, accumulation of oxidative damage markers in tissues must ideally be maintained at low levels over time, because the accumulating debris disturbs cellular functions. We investigated shell growth and cellular aging in an Icelandic population of A. islandica. Specifically, we analyzed protein carbonyl concentration as a marker for the oxidative deterioration of tissue proteins, and the accumulation of the fluorescent age pigment lipofuscin over quahog lifetime in gill, mantle and adductor muscle. The very slow growth rates of A. islandica correlate with very efficient maintenance of body proteins compared to other, faster aging bivalves. Lipofuscin granules accumulated mainly in connective tissues of gill and mantle. Lowest lipofuscin accumulation was found in the adductor muscle, and there, only outside the myofibrils. Consistent with the pleiotropic theory of aging, A. islandica seems to trade slow growth and late onset of reproduction for a very efficient autophagic potential that mitigates oxidative damage accumulation and supports long lifetime and presumably reproduction in very old ocean quahog. © Inter-Research 2007.