Octopuses are among of the most fascinating and intelligent marine invertebrates. These molluscs belong to the class Cephalopoda which also includes squid, cuttlefish, and nautilus.

Octopus

The word cephalopod comes from ancient Greek and means “head-foot,” referring to the way in which their eight arms are connected to their head, rather than their body. They have been seen using tools to protect themselves and hunt, can solve puzzles and even recognise faces.

There are over 300 known species of octopus, and they inhabit oceans all around the world, from the icy waters of the Arctic to the Southern Ocean near Antarctica. New species are being discovered every year, such as the flapjack octopus (Opisthoteuthis carnarvonensis) which lives in the deep-sea canyons near Carnarvon and was only officially described in May 2025. Octopuses vary greatly in size, he smallest known species is about 2.5cm in length and is so tiny that it can fit on a human fingertip. The giant Pacific octopus on the other hand is one of the largest species, with some weighing as much as 70kg and stretching up to 5m from arm to arm.

Octopus djinda

Octopuses are primarily nocturnal hunters, their diet consists of crustaceans, such as crabs, lobsters and shrimps, as well and molluscs such as whelks, clams and mussels. They use their strong, parrot-like beak capable to pierce through their hard shells.

They have eight arms – not tentacles, and each one can act independently, containing two thirds of their neurons, with nerve cells that allow them to taste and smell. They can regrow lost arms as well. Octopus also have a unique circulatory system, with three hearts, and blue blood! Two of the hearts pump blood to the gills, while the third circulates it to the rest of the body to the rest of the organs.

Unlike most animals that use iron-based haemoglobin to transport oxygen, octopuses use copper-based haemocyanin, which gives their blood its distinctive blue colour.

Masters of camouflage, they can rapidly change their colour and skin texture to blend in with their surroundings This is made possible by chromatophores – special pigment-containing cells that they manipulate to produce different colours and patterns. They also have skin papillae that can expand and contract, allowing them to mimic textures like rocks, coral, or sand. These adaptations serve multiple purposes, including hiding from predators, ambushing prey, communicating with other animals, startling threats, and even mimicking dangerous species like sea snakes or lionfish. Some researchers believe these changes may also reflect the octopus’s mood!

Did you know that all species of octopus are venomous? The famous blue-ringed octopus can inject a neurotoxin more powerful than cyanide through its bite, which causes paralysis and is often fatal. Thankfully, most species venom isn’t dangerous to humans; however, it can be lethal to smaller prey. As well as a venomous bite, most species can shoot ink, disorientating prey and interfering with their eyesight, sense of taste, and smell, giving the octopus a chance to escape.

Octopus are invertebrates, which means they lack a skeleton. Having a soft body means they can squeeze themselves into small crevices and holes, as long as the space is larger than their hard, parrot-like beak. When it comes to moving around, they tend to use their arms to crawl and pull themselves along, however they can also use jet propulsion, forcefully expelling water through their siphon, enabling them to move quickly through open water.

Octopuses generally have short lifespans, with their lifecycle often coming to an end shortly after mating. Males may die weeks after delivering sperm, while the females while lay thousands of eggs and spend the rest of their lives guarding them. The female will stop eating, and her body will slowly deteriorate. Her final moments spent keeping her offspring safe.