How are octopuses different from squids and cuttlefishes?

Octopuses, squids, and cuttlefishes are all members of the subclass Coleoidea, but they differ significantly in their anatomy, habitat, and behavior.

Anatomical Differences

• Arms and Tentacles: Octopuses (order Octopoda) possess eight sucker-bearing arms. In contrast, squids (order Teuthoidea) and cuttlefishes (order Sepioidea) have eight arms plus two additional tentacles that are used for capturing prey.123
• Shells: Octopuses generally lack a shell or have only a vestigial one. Cuttlefishes are characterized by a thick, internal calcified shell known as the cuttlebone, while squids possess a thin, horny internal structure called a gladius.13
• Body Shape: Octopuses typically have a saccular, round body. Squids are often streamlined for active swimming, and cuttlefishes have somewhat flattened bodies bordered by narrow fins.1423

Behavioral and Ecological Differences

• Lifestyle: Octopuses are primarily bottom-dwelling, secretive animals that crawl along the seafloor. Squids are often active, pelagic swimmers, and cuttlefishes typically inhabit shallow coastal waters.5413
• Intelligence and Tool Use: While all three groups are highly intelligent, octopuses are particularly noted for complex behaviors, including the use of tools like coconut shells for shelter.64