When you think of cephalopods (if you think of cephalopods), then two creaturs probably come to mind first: the squid and the octopus. While both are "head-footed" animals and both live in aquatic areas, these two animals differ greatly in several ways.
Can you tell the difference between a squid and an octopus by sight? An octopus has a round, large head and mantle with eight arms. While they also have a mantle and eight arms, squids have more of a triangular-shaped head - more narrow and pointed at the top.
Squid also have two fins and two small tentacles on their heads. The arms of a squid also have suckers and / or hooks on them. Squid possess a stiff structure known as a pen that acts like a flexible backbone.
Octopuses tend to live in dens on the sea floor and eat bottom-dwelling crustaceans, while squid prefer living in open oceans and eat mainly fish and shrimp. An octopus is a loner - octopuses live and hunt alone and rarely spend time with others. Squid may be solitary but sometimes they live in schools or groups.