The Galápagos tortoise or Galápagos giant tortoise (Chelonoidis niger) is a species of very large tortoise in the genus Chelonoidis (which also contains three smaller species from mainland South America). It comprises 15 subspecies (13 extant and 2 extinct). It is the largest living species of tortoise, with some modern Galápagos tortoises weighing up to 417 kg (919 lb). With lifespans in the wild of over 100 years, it is one of the longest-lived vertebrates. Captive Galapagos tortoises can live up to 177 years. For example, a captive individual, Harriet, lived for at least 175 years. Spanish explorers, who discovered the islands in the 16th century, named them after the Spanish galápago, meaning 'tortoise'. The tortoises have a large bony shell of a dull brown or grey color. The plates of the shell are fused with the ribs in a rigid protective structure that is integral to the skeleton. Lichens can grow on the shells of these slow-moving animals. Tortoises keep a characteristic scute (shell segment) pattern on their shells throughout life, though the annual growth bands are not useful for determining age because the outer layers are worn off with time. A tortoise can withdraw its head, neck, and fore limbs into its shell for protection. The legs are large and stumpy, with dry, scaly skin and hard scales. The front legs have five claws, the back legs four. (Source: Wikipedia.org, CC BY-SA)