I saw this live clam in the tidepools. It was quite large. It measured about 5 inches across the shell. It is very hard even for experts to tell clams apart since they have very similar shells. This one is either a Pacific Butter clam, or a Pacific White Venus. Clams can live for up to 30 years! And when they are this size they can filter a half gallon of water in an hour. They are filter feeders that consume microscopic debris from the water. You can see the mantle in these pictures. We see a lot of clam shells, but rarely a live clam.