The Spondylus Thorny Oyster smiling on the reef. These oysters which can grow up to 10cm in diameter are common on Indo-pacific reefs. If you look carefully, you can see the small eyes on stalks that they have developed on the edge of their mantles. If something gets too close they close their shell shut to protect themselves. To get a picture of them smiling, you have to sneak up quietly without stirring up the water too much or casting a shadow.