Starfish are not fish. Neither are jellyfish.
Starfish live underwater but that is where the resemblance between them and fish ends. They have no gills, no brain, no scales nor fins. Starfish only live in salt water and instead of blood, they pump sea water round their body for nutrients via a ‘water vascular system’.
Jellyfish, lacking in brains, blood or even a heart, jellyfish are simple animals. They have an ‘elementary’ nervous system which allows them to smell, detect light and respond to a few other stimuli. The simple digestive system of a jellyfish acts as both a stomach and an intestine. Jellyfish are about 95 percent water and will evaporate if you take them out of water.