Look also for filter feeders, the animals that take advantage of the plankton and detritus floating by in the water. Examples include clams, mussels, and barnacles. You won't see any this big on the reef flat, but you will see several different species. Look for the ring of tentacles, with which they constantly stuff sediment into their mouths. Photo courtesy Dr. Bob Richmond.
Clams are filter feeders.
They are hard to find on the reef because they close up when you approach and their shells are partly buried. That's why it's an adult treasure hunt. Explains the various zones from the beach to deep water, with several pictures of each zone. These show you more of the underwater world than you can experience at low tide.