The tridacna, also known as the giant clam, comprises the largest family of clams in the world. In the wild ocean, some species can grow to a length of 4 feet and weigh as much as 500 pounds. The beautiful colors of their mantles ranges from green to blue and deep purple. The colors are produces by a type of photosynthetic algae that lives within the clam's tissue. The algae uses sunlight to produce food for itself and for the clam. The bright colors make tridacna clams a favorite among reef aquarium hobbyists.