They are fast, they are ruthless, they are the largest fish on the planet and nearly as ancient as the oceans themselves. But by far not all sharks are as dangerous and fearsome as the great white shark or the truly creepy megalodon. In fact, the largest shark species on the planet today, the whale shark, which can grow up to 19 meters (62 feet) long feeds solely on plankton. Learn the basics about sharks, their evolution and reproduction in the video below.