Which of these animals have no brains?

Called “jellies,” this family of translucent creatures is unique. All other creatures without brains tend to be immobile, often spending their entire existence in a single spot. Jellyfish move with the ocean current. Jellyfish use this ability to propel themselves toward prey, such as plankton, in oceans throughout the world. Their ability to move also comes in handy when they need to avoid predators like fish, turtles, and seabirds. The jellyfish functions through a network of sensory nerves. Tentacles react to foreign objects with a shooting sting. That sting releases a toxin capable of neutralizing or killing the intruder.

Source: A-Z Animals