Finally, in photo 4 there is the lowly clam. It is sedentary and can easily be found in coral rocks or simply lying on the seabed. Most feed by filtering plankton out of the water. The clam is called a bivalve mollusk because it has two shells, or valves. These are held together by a ligament and are opened and closed by two powerful muscles. When a clam needs to move, it opens up and its fleshy foot emerges a bit. But should an enemy approach, it retreats into its shell and ‘clams up’!

4. The clam feeds on plankton (mouth shown)