The ocean quahog Arctica islandica is the longest-lived of all bivalve and molluscan species, animals >100 yrs are common in many populations, and reported maximum live span is 374 yrs (Iceland population). Based on the Free Radical-Rate of Living theory by Pearl (1928) and Harman (1956) I am studying random bouts of self-induced metabolic rate depression (MRD), which will lower generation rates of reactive oxygen species. The animals induce MRD by spontaneous burrowing into the sediment and closing their shellls. This may be an energy saving and life prolonging strategy in the ocean quahog. Nitric oxide (NO) is an important signalling molecule and also a free radical of potential importance. In vertebrate cells NO has been recognized as an important parameter that controls mitochondrial respiration by directly inhibiting with the oxygen binding site of cytochrome-c oxidase activity (Boveris et al., 2001, Turrens, 2003). Nitric oxide is a proven signal molecule in invertebrates like molluscs whereas the concentration of NO in the cells and the hemolymph is dependent on its oxygenation status. I am investigating a model for a prospective role of NO in the self-induced MRD in A. islandica :when the clam buries under, hemolymph Po2 declines in the closed shell, leading to an increase of c[NO] in the hemolymph. NO could then diffuse into the cells to reduce mitochondrial respiration by inhibition of cytochrome-c oxidase and to initiate MRD in long-lived A. islandica.