Squid vs Octopus
Most of the time, people are confused about the difference between a squid and an octopus. Though they both are residing in salty water in the tropics and are both related to mollusks or snails, there still lies some dissimilarity.
To start off, octopuses could grow from one centimeter to more than five meters in size while squids grow in size from one centimeter to twenty meters. And even if they belong to the mollusks family, they both do not have shell. Octopuses do not actually have any bone in their body while squids have pen, which is the hard but flexible structure that serves as the backbone. In the same manner, octopuses do not have fins while squids have two which are located on their heads. Both have 8 arms but squids have two specialized tentacles that have hooks and sucker rings.
Most of the time, you would find octopuses inside caves or holes of the sea floor while squids are fond of living in the open sea. And given their own habitats, octopuses feed themselves with the sea bottom crustaceans while squids feed on shrimps and fishes. The octopuses always live by themselves, thus they are solitary creatures. On the other hand, squids may also live by themselves but are mostly living in large schools. Some squids though may live in schools during their early life but tend to live in solitary as they age.
Both male squids and octopuses fertilize the female by using a special arm that transfers the sperm to the special layer in the female beak. But then squids usually reproduce in huge schools/groups. Their eggs are usually being attached to seaweeds or sometimes in the sea floor. After spawning, squids die. Octopuses on the other hand, guard the eggs in their dens and sometimes even create rock wall to seal their caves to protect their eggs. Octopuses do not die immediately after spawning since they guard their eggs until they hatch, which is usually 30 to 360 days, depending on the species.
Usually, squids are larger than octopuses. They also live longer since squids have a lifespan of 9 months to 5 years while octopuses may live for 6 months to 5 years.