What is the difference between a squid and an octopus?


Both groups are remarkably brainy molluscs, especially compared to their relatives including snails, clams and slugs. They have complex nervous systems which, among other things, intricately controls their colour-changing skin.

A recent study of Humboldt squid suggested they have a simple language of patterns displayed across their bodies. Another piece of research on oval squid in Japan has recently shown that, just like octopuses, squid can also match their body colour to their surroundings to hide from predators.

There are, however, plenty of differences between octopuses and squid. To tell them apart, all you need to do is count their numerous appendages. Octopuses have eight arms with sensitive suckers arranged all the way to the tip. Meanwhile, squid have eight arms plus an additional pair of limbs with suckers just at the ends. These are tentacles that they shoot out, like a chameleon’s tongue, to grab and drag in prey.

A photograph of an octopus on a shallow seafloor

Most octopuses are solitary and live close to the sea floor © Getty images

There are around 300 species of octopuses, and a similar number of squid which occupy different ocean habitats. Most octopuses live close to the seabed, with a few exceptions like blanket octopuses and argonauts. Usually, they’re solitary and often thoroughly antisocial (in aquariums they tend to eat each other).

The exceptions are two locations in Australia, nicknamed Octopolis and Octlantis, where octopuses have been found living rather awkwardly together in close neighbourhoods. In contrast, squid swim through open seas, often in coordinated shoals.

A photograph of a school of Caribbean Reef Squid

A shoal of Caribbean Reef Squid ( Sepioteuthis sepioidea) hovering over a tropical coral reef off the island of Roatan, Honduras. © Getty images

Octopuses and squid also differ in the way they produce offspring. For octopuses, male-female pairs mate at arm’s length. The female then lays her eggs in a safe spot on the seabed and watches over them until they hatch. Squid mate in groups and leave their eggs to fend for themselves, stuck to seaweed, rocks and corals.

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Asked by: Andrew White, Hull

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