Sharks: Amazing Pictures & Interesting Facts Children Book About Sharks Getting to know sharks The earliest sharks (members of the Elasmobranchii subclass) are over 420 million years old. There are over 500 species of sharks. Sharks come in many sizes. There are sharks as small as 17 cm. Also, the largest fish in the world is a shark--the whale shark or Rhincodon typus is around 12 meters in length. Sharks are related to rays. Modern sharks belong to the clade (or group) Selachimorpha or Selachii. The word shark is thought to be of Yucatec Mayan origin, and could mean sea fish, predator, or villain.