The animal known to have the longest lifespan is the ocean quahog, a species of clam that can live for over 500 years. Some individuals have been found to be more than 500 years old, making them the oldest known living animals. Other long-lived creatures include certain species of tortoises and whales, but the ocean quahog holds the record. Their incredible longevity is primarily due to their slow growth rate and the favorable environmental conditions in which they live, primarily in the North Atlantic Ocean.