Giant Clam
There are a number of varieties of giant clams. This brilliant blue one is striking. Amazingly, underwater, they aren’t all that obvious to spot. You can see the valve there on the left. They get quite large. This one is two hands wide. He’s been around long enough to have been almost totally encrusted with coral. It is a veritable vegetarian paradise around here. I suppose this one would make a large clam chowder.