Of the 15,000 species of bivalves known as clams, some have life cycles of only one year. Individuals of one species called the ocean quahog, or Arctica islandica, however, are among the oldest living animals on Earth, with one captured specimen measured to be more than 500 years of age.
Researchers usually measure the age of clams by the growth rings on their hinge ligaments or the outside of the shell. An ocean quahog clam found off the coast of Iceland in 2006 was first determined to be 405 years old. However, a later, more comprehensive analysis confirmed that the clam was actually 507 years old. Because the clam had to be opened to determine its age, it died, or it might have lived even longer. The clam was nicknamed Ming because it was conceived during the Chinese Ming Dynasty. Ming's status as the world's oldest animal was confirmed using the carbon-14 dating method.
Clams have two equal shells that are held together with a ligament and opened and closed with muscles. They have strong, burrowing feet that they use to bury themselves in sand. They are filter feeders that use siphons to draw water into themselves for feeding and breathing. They vary in size from nearly microscopic species to giant clams that can weigh more than 440 pounds. Many clam species inhabit shallow fresh and salt waters, but one species of clam in the Pacific Ocean has been found at a depth of 16,000 feet.