We just learned about the Rhopalium.
Another part of a jellyfish is the Ocelli.
In the parrs of the jellyfish's bell where it dents in called the rhopalium, sometimes a jellyfish will have eyes called the ocelli.
They are very simple and do not have a lot of parts like human eyes, but they can sense some darkness and light, and use that to swim toward or away from something.
(from: wikipedia - carybdeida)
Kid Facts - Blast from the past: Cephalopod Eyes