Which marine animal is the largest living bivalve mollusc?

The giant clam is the largest living bivalve mollusc. Tridacna gigas can exceed 1.2 metres in length and weigh more than 200 kilograms, making it an exceptional member of the clam family.

Giant clams live in shallow coral-reef environments of the Indo-Pacific. Their mantle contains microscopic algae called zooxanthellae, which use sunlight to produce energy and provide much of the clam’s nutrition. The clam also filters tiny particles from seawater, so it combines photosynthetic and suspension-feeding lifestyles.

People sometimes confuse the giant clam with the geoduck because geoducks are also very large bivalves. Geoducks are famous for their long siphons, but giant clams have a much greater shell size and total mass. Giant clams are hermaphroditic, releasing sperm and eggs at different times to reduce self-fertilisation.