They only appear in the level Lots O'Jellyfish! as an enemy.
They appear as enemies but resemble real-life ones.
Super Mario Galaxy series
If you get too close to a Jellyfish and touch it, it will shock you. You can defeat these enemies by throwing a shell at them or spinning into them. Starbits will only make them bounce a little, showing that the small attack doesn't hurt them. There are larger variants called Jammyfish which are electric and have no faces and can only be defeated by Shells.