Bivalves: Bivalvia

Physical characteristics: This largest of all living bivalves measures up to 53.9 inches (1,369 millimeters) long and weighs up to 579.5 pounds (262.8 kilograms). The whitish valves are thick, heavy, and have four to six distinct folds. The inside surfaces of the valves are white and smooth. The mantle is brightly colored, ranging from yellowish brown to olive green with shiny blue green spots. The openings to the siphons are quite distinctive.

Geographic range: They are found in the Southwestern Pacific from Philippines to Micronesia.

Habitat: Giant clams live at depths of 6 to 66 feet (2 to 20 meters) on coral reefs, partially buried in sand or rubble.

This largest of all living bivalves measures up to 53.9 inches (1,369 millimeters) long and weighs up to 579.5 pounds (262.8 kilograms). (Illustration by Barbara Duperron. Reproduced by permission.)

Diet: Giant clams rely on the nutrients made by algae that live only in the tissues of the clam's mantle. Giant clams supplement this diet with tiny bits of plants and animals floating in the water.

Behavior and reproduction: Adults move about coral reefs with their valves hinge-down. The valves remain open unless the clam is threatened. Larger individuals cannot completely close their valves.

Giant clams develop first as males and later become females. Eggs and sperm are released into the water, where they are fertilized. The life span is unknown but is estimated to range from decades to one hundred years.

Giant clams and people: People living on Pacific Islands harvest giant clams and eat the muscle that closes the valves. Giant clam shells have long been used to make mallets, hoes, scrapers, and wash basins. They are also raised to sell to people that keep them in salt water aquariums.

Conservation status: Giant clams are considered Vulnerable by the IUCN, which means they face a high risk of extinction in the wild. ∎