Flexi Says: The movement a useful innovation for cnidarians that was characterized by the evolution of medusa from the polyp. That made it easy for these predatory carnivores to flourish in the ocean habitat. It’s the flow created by swimming that brings prey. The cnidarian body is very effective for creating the flow which enables the animal to feed. As the jelly’s bell pulses, the water flows in under the bell margin through the tentacles, bringing food particles in contact with both the tentacles and the oral arms, where nematocysts can shoot their harpoons to capture prey.