The giant clam gets only one chance to find a nice home. Once it fastens itself to a spot on a reef, there it sits for the rest of its life.

These bottom-dwelling behemoths are the largest mollusks on Earth, capable of reaching 4 feet in length and weighing more than 500 pounds. They live in the warm waters of the South Pacific and Indian Oceans.

Giant clams achieve their enormous proportions by consuming the sugars and proteins produced by the billions of algae that live in their tissues. In exchange, they offer the algae a safe home and regular access to sunlight for photosynthesis, basking by day below the water's surface with their fluted shells open and their multi-colored mantles exposed.