Random visit Whitsunday Islands National Park Un peu d'info en Fr. sur les Tridacne géant ou bénitier géant (Tridacna gigas) Excellent link with lots of clear information and superb underwater pictures: Giant Clams of the Great Barrier Reef From Giant clam in Wikipedia: “The giant clam (Tridacna gigas) or traditionally, pa’ua, is the largest living bivalve mollusc. One of a number of large clam species native to the shallow coral reefs of the South Pacific and Indian oceans, they can weigh more than 227 kilograms (500 pounds) and measure as much as 1.2 metres (4 feet) across, and have an average lifespan in the wild of 100 years or more. Sessile in adulthood, the creature's mantle tissues act as a habitat for the symbiotic single-celled dinoflagellate algae (zooxanthellae) from which it gets its nutrition. By day, the clam spreads out its mantle tissue so that the algae receive the sunlight they need to photosynthesize.” Note that I don't know which species of giant clam this is.