These clams are enormous, reading four feet long and over 400 lb. They are becoming rare due to over harvesting. They are taken for their shells, for meat, and for the aquarium trade. The brilliant colors of the mantels are due to algae that live symbiotically with the clam. The algae help generate food for the clam, the clam opens exposes them to sunlight during the day and protects them in the shell at night.