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Bivalves: Bivalvia

Giant Clam (tridacna Gigas): Species Accounts

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. ∎



Brusca, Richard C., and Gary J. Brusca. Invertebrates. Sunderland, MA: Sinauer Associates, 2003.

Gordon, D. G. Field Guide to the Geoduck. The Secret Life of the World's Biggest Burrowing Clam—from Northern California to Southeast Alaska. Seattle, WA: Sasquatch Books, 1996.

Gordon, D. G., N. E. Blanton, and T. Y. Nosho. Heaven on the Half Shell. The Story of the Northwest's Love Affair with the Oyster. Portland, OR: West Winds Press, 2001.

Nalepa, Thomas F., and Donald W. Schloesser, eds. Zebra Mussels: Biology, Impacts, and Control. Boca Raton, FL: Lewis Publishers, 1993.

Rehder, H. A. National Audubon Society Field Guide to North American Seashells. New York: Alfred A. Knopf, 1997.


Doubilet, D. "Black Pearls of French Polynesia." National Geographic (June 1997): 30-37.

Zahl, P. A. "The Magic Lure of Seashells." National Geographic (March 1969): 386-429.

Web sites:

"Class Bivalvia (Bivalves and Clams)" http://animaldiversity.ummz.umich.edu/site/accounts/information/Bivalvia.html (accessed on May 1, 2005).

Welcome to the Zebra Mussell Page. http://nas.er.usgs.gov/taxgroup/mollusks/zebramussel/ (accessed on May 1, 2005).

Additional topics

Animal Life ResourceMollusks, Crustaceans, and Related SpeciesBivalves: Bivalvia - Physical Characteristics, Behavior And Reproduction, Bivalves And People, Conservation Status, Black-lipped Pearl Oyster (pinctada Margaritifera): Species Accounts - GEOGRAPHIC RANGE, HABITAT, DIET