More arms, different shapes? It’s tough trying to get to the bottom of what exactly separates octopuses and squid. Both are in the class Cephalopoda and inhabit the majority of the ocean – but each has their own physical differences, their own habitat preferences and unique behaviour. It’s much the same as the manatee and dugong case – animals similar enough to get the two mixed up, yet different when you dig deeper into their anatomy and how they function.
UW360 takes a look at the incredible differences between octopuses and squid:
Octopuses are famous for being without a stiff bone in their bodies, which enables them to be able to squeeze through tight gaps. Squid, by contrast, possess a stiffer structure known as a pen, which acts like a flexible backbone that runs the length of the animal’s body and stabilises it whilst it’s swimming.
The makeup of both animals is similar, yet different. An octopus has a mantle, a head, eight arms equipped with one or two rows of suckers but with no hooks or sucker rings. A squid has two fins, a mantle, a head, eight arms and two tentacles, which are equipped with hooks and suckers or sucker rings.
Octopuses tend to prefer living in dens on the ocean floor, from the shallows to the deep (dependent on the species). Some live in bottles or other rubbish that has found its way to the bottom of the ocean floor. Squids live in the open ocean, from the shallow coasts to deep in the dark depths of the sea.
Techniques for hunting vary between the two. Octopuses grab their prey and pierce through their shell to inject a paralysing venom. They then dissolve and loosen the meat with their saliva, using their powerful beak and mouth to rip the prey apart. Squid catch food with their long tentacles and consume it in chunks.
Octopods have no fins, though there is an argument that some of the deep-sea dwelling species do in fact have them. Squid have fins on their head. The colossal squid, for example, has a paired tail fin attached to the upper surface of its mantle and is made up of muscle – the squid uses its paired fin to swim forward. Massive and muscular, the fin enables the colossal squid to move rapidly through the ocean, but in most squid, the paired tail fins are used for changing direction rather than for propulsion.
Both animal types use a different mating strategy. Male octopuses use a specialised arm called a hectocotylus to transfer sperm to the mantle cavity of a receptive female. The female then lays a string of fertilised eggs on the roof of her den which she guards and cleans – and even aerates with water expelled from her siphon – anywhere from 30 days to a year, depending on the species. The female may even build a wall of rocks to seal off the den, where she will remain until the eggs have hatched and she journeys off to die.
Instead, squid mate in large groups, attaching their egg capsules to the seabed or to seaweed. Similar to octopods, squid die shortly after reproducing.