Jellyfish

Jellyfish existed before fish, even before dinosaurs. It is estimated that they are more than 500 million years old. They are plankton, which means that they follow the ocean currents. Jellyfish lack both a brain and a heart, but they are still capable of eating large fish. They can sense smells and movements in the water, but most jellyfish do not hunt their prey. Instead, they are almost like spiders, spreading their tentacles and waiting for animals to be caught.