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 bilaterally symmetric body with two eyes and a beaked mouth in the center of their eight arms. One of their most amazing abilities is to change shape, allowing them to squeeze through tiny spaces.

These clever creatures live in many ocean habitats, from coral reefs to the seabed, and some even live in the intertidal zone or at abyssal depths. Most octopuses grow quickly, become mature fast, and have short lives. They are skilled hunters, eating crustaceans, bivalves, gastropods, and fish. To protect themselves, they can release ink, hide using camouflage, or jet away quickly.

All octopuses are venomous, but only the blue-ringed octopuses can be dangerous to humans. Octopuses have appeared in stories and myths for centuries, such as the kraken of Norway and the Ainu's Akkorokamui. In some cultures, they are a popular food. Their intelligence and unique abilities make octopuses fascinating creatures to learn about.

Etymology and pluralisation

See also: Plural form of words ending in -us

The word octopus comes from Ancient Greek, where oktōpous means "eight-footed." This combines the words for "eight" (oktō) and "foot" (pous).

In English, the usual way to say more than one octopus is octopuses. Some people also say octopodes or octopi, but octopuses is the most correct and commonly used form.

Anatomy and physiology

The giant Pacific octopus is often considered the largest octopus species. Adults typically weigh between 10–50 kg and can have an arm span of up to 4.8 m. Much larger sizes have been reported, with one specimen weighing as much as 272 kg and having an arm span of 9 m.

Octopuses have an elongated, soft body with eight flexible arms. They are bilaterally symmetrical, with a head containing both the mouth and brain. The mouth has a sharp beak and is surrounded by the arms, which are used to walk on the sea floor and to forage for food. The skin can change color to help the octopus blend into its surroundings. Each arm is covered with suction cups that allow the octopus to grip objects and navigate through tight spaces. Octopuses also have well-developed eyes similar to those of fish, helping them see their environment clearly.

Life cycle

Octopuses have two sexes and reproduce using special body parts. The male uses a special arm called a hectocotylus to place packets of sperm into the female. The female then lays many eggs, which she protects until they hatch. Most young octopuses start life floating in the water before settling on the ocean floor.

Octopuses live relatively short lives, usually up to four years. Their lifespan can be even shorter, sometimes finishing in just a few months. As they age, octopuses become weaker and may stop eating, eventually leading to their natural end.

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, where temperatures reach −1.8 °C (29 °F). 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, though some live in groups when there is lots of food and few places to hide. The Larger Pacific striped octopus is known to live in groups of up to 40. Octopuses hide in dens, which are often in rocky or hard structures, and small species may use old shells or bottles.

Octopuses hunt for food like crustaceans, bivalves, fish, and even other octopuses. They find prey by feeling around with their arms and may hide to ambush it. Some octopuses drill into shells to eat, while others swallow their food whole. They can also change colour and texture to hide from predators or to scare them away. When 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 evolved from ancient sea creatures called molluscs around 530 million years ago. Over time, they developed unique features such as their soft bodies and eight limbs. Because their bodies are mostly soft, fossil records of octopuses are scarce. 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

Ancient 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 they can be scary. Some big octopuses have been known to 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, which can be risky if not prepared carefully.

Science and technology

Scientists are very interested in octopuses because of their cleverness and 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 also help engineers make new kinds of robots that can move in smart ways.