What's the difference between octopuses and fiish?

The difference between octopus and fish can be explained in terms of the anatomy and physiology. Firstly, I want to tell you what is the octopuses?
Octopus is categorized under Phylum Mollusca, Class Cephalopoda and is found in oceans throughout the world.  But Fish belongs to Phylum Cnidaria. Mouth opening is surrounded by tentacles which are used to kill their prey. These are the pictures of octopus and jelly fish to see the difference.