Differences between Octopus and Squid

Octopus vs. Squid

Octopuses and squids are cephalopods, a class of marine mollusks, that are known for their intelligence. Although they share some similar features, such as multiple arms and the ability to expel ink, they have many distinct differences in their anatomy, behavior, and habitats. There are around 300 species of octopus and also about 300 species of squid.

Comparison Table

Category	Octopus	Squid
Body Shape	Round, bulbous mantle without fins.	Torpedo-shaped mantle with two fins.
Appendages	Eight arms with suckers along their entire length.	Eight arms and two longer tentacles with suckers or hooks only at the ends.
Internal Structure	Entirely soft-bodied with no internal shell.	Possesses a small, flexible internal shell-like structure called a pen.
Locomotion	Primarily crawls along the seabed using its arms; uses jet propulsion for rapid escape.	Swims in the open ocean using its fins for slow movement and jet propulsion for speed.
Habitat	Lives on the ocean floor, often in dens or crevices.	Inhabits the open ocean, from near the surface to great depths.
Lifespan	Typically 1 to 3 years.	Generally 1 to 5 years, though some deep-sea species may live longer.

Venn diagram comparing Differences between Octopus and Squid

Anatomy and Appearance

The most noticeable difference between octopuses and squids is the shape of their bodies, or mantles. An octopus has a round, sac-like mantle and lacks fins. Because they are boneless, they are able to fit into very small spaces. In contrast, a squid has a more rigid, torpedo-shaped mantle with two fins on the side, which they use for stabilization and steering at slower speeds. Squids also possess a flexible, feather-shaped internal structure called a pen, which acts as a sort of backbone, a feature octopuses lack.

Another key distinction is their limbs. Octopuses have eight appendages, all of which are classified as arms. These arms are lined with suckers along their entire length. Squids, on the other hand, have ten appendages in total: eight arms and two longer tentacles. The two tentacles are used to snatch prey from a distance and typically have suckers only on their club-like ends.

Habitat and Locomotion

Their body structures are well-suited to their respective environments. Octopuses are primarily bottom-dwellers, living on the seafloor in a variety of environments, from shallow tide pools to abyssal depths. They typically move by crawling along the ocean floor, using their flexible arms to navigate the terrain. While they can use jet propulsion to escape predators by expelling water from their mantle through a siphon, it is not their primary mode of movement.

Squids are generally found in the open ocean, from near the surface to the deep sea. They are active swimmers, using their fins for slower movements and jet propulsion for fast travel, which allows some species to even launch themselves out of the water for short distances. While both are found in saltwater across the globe, octopuses are often solitary animals that take shelter in dens, whereas squid can be found alone or in large schools.

Lifespan and Reproduction

Both octopuses and squids generally have short lifespans. For most octopus species, life expectancy is between one and three years. Larger species, such as the giant Pacific octopus, may live up to five years. Squids have a slightly more varied lifespan, ranging from about one year for smaller species to five years or more for some larger, deep-sea varieties. For most species of both octopus and squid, the males die shortly after mating, and the females die after laying and caring for their eggs.