The biggest shark is the Whale shark but they only eat small fishy things and shrimps. There is a new aquarium in London which is very good for seeing sea-life. I have but only on video. If you hold them the right way they can't pinch you at all. Hold them from the back of their shell just behind their front pincers.
Many sea creatures eat the plankton.
If they are ever in danger, they swim back home as fast as they can and hide in the deadly stinging tentacles of anemonies. The anemone gets pieces of the clown fishs' food so they are both happy.