Octopuses and Squids are both head-footed aquatic animals (cephalopods) but they differ in their physical characteristics, habitat and behavior.
An octopus has a round head and a mantle along with eight arms. The arms are endowed with one or two rows of suckers but these never have hooks or sucker rings. Squids are also cephalopods with a triangular shaped head, a mantle and eight arms. Along with that they have two fins on their head and two tentacles. The arms of a squid are endowed with hooks and/or suckers or sucker rings. The tentacles are arranged in pairs.