Octopuses and squid are actually two very different marine organisms, though they are both classified as being cephalopods. Even though they are put in the same technical classification, their physical characteristics as well as behaviors and habits differ quite a bit from one another.
Octopuses tend to have round heads with arms that have one or two rows of “suckers†without hooks and suck rings. Squids on the other hand, although they too are cephalopods, have a triangular head and their endowed arms come with hooks as well as suckers. The tentacles which squids have are typically arranged in individual pairs.