Octopus

An octopus (pl.: octopuses or octopodes) is a soft-bodied, eight-limbed mollusc of the order Octopoda (/ɒkˈtɒpədə/, ok-TOP-ə-də). They belong to the class Cephalopoda along with squids, cuttlefish, and nautiloids. Octopuses have a body with two eyes and a beaked mouth in the middle of their eight arms. One of their best tricks is changing shape, which lets them fit through very small spaces.

These clever animals live in many ocean places, from coral reefs to the seabed, and some even live in the intertidal zone or at abyssal depths. Most octopuses grow fast, become adults quickly, and do not live very long. They are good hunters and eat crustaceans, bivalves, gastropods, and fish. To stay safe, they can squirt ink, hide with camouflage, or zoom away in a flash.

All octopuses are venomous, but only the blue-ringed octopuses can harm people. Octopuses have been part of stories and myths for many years, like the kraken of Norway and the Ainu's Akkorokamui. In some places, they are enjoyed as food. Their smarts and special skills make octopuses very interesting to learn about.

Etymology and pluralisation

See also: Plural form of words ending in -us

The word octopus comes from Ancient Greek. It means "eight-footed." This name combines the words for "eight" and "foot."

In English, we usually say octopuses when we mean more than one octopus. Some people also say octopodes or octopi, but octopuses is the most common and correct way to say it.

Anatomy and physiology

The giant Pacific octopus is one of the largest octopus species. Adults usually weigh between 10 and 50 kg and can have arms stretching up to 4.8 m. Some very big ones have been found, with one weighing as much as 272 kg and having arms up to 9 m long.

Octopuses have a soft body with eight flexible arms. They have a head with a mouth and a brain. The mouth has a sharp beak and is surrounded by the arms, which they use to walk on the sea floor and find food. Their skin can change color to hide in their surroundings. Each arm has suction cups that help them grip things and move through narrow spaces. Octopuses also have good eyes, similar to fish, which help them see their environment clearly.

Life cycle

Octopuses have two sexes. The male uses a special arm to give the female packets of sperm. The female lays many eggs and guards them until they hatch. Most baby octopuses float in the water at first, then settle on the ocean floor.

Octopuses do not live very long, usually up to four years. Sometimes they live only a few months. As they get older, they grow weaker and may stop eating, and this leads to their natural death.

Distribution and habitat

Octopuses live in every ocean, adapting to many different habitats. Young common octopuses start in shallow tide pools, while the Hawaiian day octopus (Octopus cyanea) lives on coral reefs, and argonauts float in pelagic waters. Some species, like Abdopus aculeatus, stay near shore in seagrass beds, and others live deep under the water. The spoon-armed octopus (Bathypolypus arcticus) can be found 1,000 metres deep, and Vulcanoctopus hydrothermalis lives around hydrothermal vents at depths of 2,000 metres.

Certain octopuses can even survive in the cold waters of the Antarctic. No octopus species live in fresh water. The cirrate species usually swim freely in deep water, and while many live at bathyal and abyssal depths, there is only one confirmed record of them in the hadal zone; a dumbo octopus (Grimpoteuthis) was photographed at a depth of nearly 7,000 metres.

Behaviour and ecology

Octopuses usually live alone, but some live in groups when there is lots of food and few places to hide. The Larger Pacific striped octopus can live in groups of up to 40. Octopuses hide in dens, often in rocky or hard places, and small ones may use old shells or bottles.

Octopuses hunt for food such as crustaceans, bivalves, fish, and sometimes other octopuses. They find prey by feeling around with their arms and may hide to catch it. Some octopuses drill into shells to eat, while others swallow their food whole. They can change colour and texture to hide from predators or to scare them away. If threatened, they may release ink to confuse a predator and escape. Some octopuses can even grow a new arm if one is lost.

Main article: Cephalopod intelligence

Evolution

Further information: Evolution of cephalopods

The name Octopoda was given to octopuses in 1818 by a scientist named William Elford Leach. There are about 300 known species of octopuses. They are part of a group called Cephalopoda, which also includes squids and cuttlefish.

Octopuses came from ancient sea creatures called molluscs about 530 million years ago. Over time, they developed special features like soft bodies and eight limbs. Because their bodies are soft, there are not many fossils of octopuses. Unlike some other sea creatures, octopuses do not have hard shells, which makes them different from their relatives like nautiloids.

Relationship to humans

Cultural significance

Long ago, people knew about octopuses and often showed them in art. They appeared on coins in the Minoan civilization and in designs from Mycenaean Greece. Some cultures, like in Hawaii, have stories where the octopus plays a big role. Legends such as the kraken, a huge sea monster, and Medusa, who had snake-like hair, are often linked to octopuses. In Japan, old stories and art sometimes show octopuses in exciting or important ways.

Danger to humans

Octopuses usually stay away from people. But sometimes, big octopuses can surprise divers by grabbing onto them. Most octopuses have venom, but only the blue-ringed octopus has venom that can be very dangerous to humans. Their bite is usually small and not painful, but their venom can cause serious problems. Thankfully, if help comes quickly, most people recover.

As a food source

Many parts of the world enjoy eating octopus. People catch them in many ways, like using traps or nets. In some places, like Korea, people even eat live octopus.

Science and technology

Scientists study octopuses because they are very clever and have unique bodies. They can change colors to hide or to communicate. Some scientists think octopuses might be as smart as some animals we don’t usually think of as very intelligent. Their abilities help engineers make new kinds of robots that can move in smart ways.