What are Cephalopods?
Cephalopods are a kind of mollusk that includes mainly squid and octopus. The first cephalopods probably evolved from simpler animals like worms around 500 million years ago. At that time, all animals except arthropods still lived in the ocean, and even today all cephalopods still live in the ocean.
"Cephalopod" means "headfoot" in Greek, because cephalopods don't really have bodies, just heads and feet. All cephalopods, like worms and arthropods, have bilateral symmetry.