The longest living animal is the ocean quahog, a type of clam found in the North Atlantic Ocean. These clams can live for over 400 years, with the oldest known specimen living for 507 years. The reason for their longevity is not fully understood, but it is believed to be due to their slow metabolism and low activity levels. Other long-lived animals include the bowhead whale, which can live for over 200 years, and the Galapagos tortoise, which can live for over 100 years.