Tubba-taha reef, Sulu Sea, Philippines.
This particular variety of clam (Tridacna species), with its brilliant blue mantle, is a common sight on shallow Philippine reefs. It measures about six inches from end to end. In this photo the fleshy mantle is entirely exposed, but patience is required to see the clam in this state-- the clam will abruptly close its shell with only a minor change in light, such as a shadow. Specialized cells called ocelli along the outer edge of the mantle are responsible for light reception.
Jeffrey N. Jeffords (photographer; copyright holder; identification)
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