The oldest mollusc, indeed the longest-lived non-colonial animal discovered, is a quahog clam Arctica islandica, which had been living on the seabed off the north coast of Iceland until it was dredged by researchers from Bangor University's School of Ocean Sciences, Wales, UK in 2006. On 28 October 2007, sclerochronologists from Bangor announced that they had studied the annual growth rings in the shell and determined the clam to be between 405 and 410 years old. The clam was nick-named 'Ming' after the Chinese dynasty in power when the clam was born!
'Non-colonial' means excluding all animals such as coral and is only needed to be absolutely correct.
The team who made the discovery were part of the EU Millennium project studying cilmate change over the past 1,000 years - changes that are recorded in shells.
Comments below may relate to previous holders of this record.