Question: Why is a jellyfish and starfish not a type of fish.

Lauren Laing answered on 11 Mar 2016:

Hi Freddie and Charlie, This is a great question!

Fish are a type of aquatic vertebrates. They have gills, fins and scales; and the fact that they live only in the water make fish different from other animals. Fish are cold-blooded, with the exception of Tuna family and the Mackerel shark family. They also spend all of their lives in the water.

Jellyfish are in fact plankton; they have no bones, brain, or heart. To see light, detect smells and orient themselves, they have basic sensory nerves at the base of their tentacles. Some jellyfish make their own light; they glow or give off flashes of light. Most jellyfish use it as a defence against predators. Also, did you know, Jellyfish are about 98 percent water?

For Starfish, they live underwater, but that is where their similarities to fish end. They do not have gills, scales, or fins. Starfish can only live in seawater, while fish can live in fresh water also. Starfish use sea water, instead of blood, to pump nutrients through their bodies via a ‘water vascular system.’ Starfish are related to sea urchins and sea cucumbers.