Squids and octopuses are both head-footed cephalopods, but their behavior, habitat and physical characteristics are different. Both are blue-blooded aquatic animals, as their blood contains copper and has oxygen-carrying molecules, and they both move by jet propulsion and live in salty waters in temperate zones. They both squirt ink, but it's different colors. Squids produce blue-black ink while octopuses squirt black ink.
Squids and octopuses are from different orders: Octopuses belong to the order octopoda, while squids fall under the teuthida order. While both octopuses and squids have eight sucker-lined arms, the latter have two longer tentacles that they use to capture prey. The octopus uses its arms to pierce the shell and injects poison to its prey, causing paralysis. Octopuses are solitary animals, living in dens on the sea floor and feeding on bottom-dwelling crustaceans. Squids, on the other hand, swim and live in the open ocean and eat shrimp and fish. Some squids are bottom-dwellers, but these are likely scavengers.
Unlike squids, octopuses don't have a hard shell or stiff bone in their body. Squids have a stiff structure known as a pen that serves as their backbone. They also tend to live longer and have a life expectancy of nine months to five years. Octopuses have a life span of one to three years.