Common octopus

The common octopus lives in the sea.

It is very smart. It can learn to open a jar. It can even recognize people!

This animal is a great hunter. It hunts at dusk. It likes to eat crabs. It can also eat small shells.

An octopus uses a hard beak. It uses the beak to break shells. It also has venom to catch food. This helps it hunt well.

It can change its color. This helps it hide. It can blend in with the rocks. This keeps it safe.

An octopus can make a garden. It collects shells and rocks. It is a very busy animal.

The common octopus is a very smart sea animal.

It lives in many warm and cool oceans. These animals can grow quite large. They can live for one or two years.

This octopus is a clever hunter. It hunts when the sun goes down. It likes to eat crabs and crayfish. It uses a hard beak to break shells. It also uses venom to catch prey.

To hide, it can change its color. This helps it blend into the rocks.

Octopuses have very large brains. They can learn to unscrew a jar. They can even recognize people! They also make "gardens" with shells and rocks.

An octopus has three hearts to move blood. One main heart sends blood to the body. Two smaller hearts help the gills. The gills are parts that take oxygen from water.

The octopus uses its mantle to pump water over its gills. This helps it breathe while it lives on the sea floor.

The common octopus is a very smart sea animal.

It belongs to a group called cephalopods. These creatures are found in many different oceans. They live in the eastern Atlantic and the Mediterranean Sea. You can also find them near the Black Sea. They live from the coast of England to South Africa. Some live near the Azores and Canary Islands. They are also common in the Western Atlantic.

Scientists study them because they are so intelligent.

An octopus has a special way of breathing. It uses gills to take oxygen from the water. The gills have many tiny folds called lamellae. These folds create a large surface area. This helps the octopus catch more oxygen. Water moves into a space called the mantle cavity. The water flows over the gills and out through a funnel. Much of the oxygen also enters through the octopus's skin. When the octopus is resting, its skin takes in 41% of its oxygen.

Moving around requires a lot of energy. The octopus often crawls along the rocky sea floor. This type of movement increases its need for oxygen. To help, its main heart pumps more blood with each beat. Sometimes the octopus swims using a jet mechanism. It creates high pressure inside its mantle cavity to push itself forward. This can be hard on its body. The high pressure can squeeze the vessels that carry blood. Because of this, swimming is not a sustainable way to travel for long.

To move blood, the octopus uses three hearts. One large heart sends oxygen-rich blood to the body. Two smaller hearts are called branchial hearts. These sit next to the gills. The branchial hearts pump blood through the gills to get oxygen. Then, the blood flows back to the main heart. The blood contains a substance called hemocyanin. This is a copper-rich protein that carries oxygen. It is different from the iron-rich hemoglobin found in humans.

These animals are famous for being very clever. An octopus has about 500 million neurons in its body. This is similar to the number of neurons in a dog. They can learn to unscrew a jar or raid lobster traps. They can even recognize individual people. Some octopuses even make "gardens" out of shells and rocks.

This behavior is so unique it inspired a Beatles song. They are truly amazing hunters of the deep sea.

The common octopus, known scientifically as *Octopus vulgaris*, is a highly intelligent mollusk within the class Cephalopoda.

These creatures are famous for their complex nervous systems and remarkable problem-solving abilities. They inhabit a vast range of marine environments, from the Mediterranean and Black Seas to the southern coast of South Africa. Their distribution also includes the eastern Atlantic, the Azores, and the Canary Islands. They are also frequently found in the Western Atlantic. Because of their unique biology, they are among the most studied octopus species in the world.

To survive in diverse environments, the common octopus has evolved specialized physiological mechanisms. They prefer shallow, rocky coastal waters, often staying at depths of no more than 200 meters. While they can tolerate various temperatures, they prefer ranges between 10 and 25 degrees Celsius. In warmer seasons, they may migrate to deeper waters to find cooler temperatures. They must also manage oxygen availability, which changes based on water pressure and temperature. This relationship is described by Henry's law, which states that gas concentration in a liquid is proportional to pressure and solubility.

Respiration in the common octopus is a complex process involving gills and skin. The gills consist of branchial ganglia and many folded structures called lamellae. These lamellae are organized into primary, secondary, and tertiary folds to maximize surface area. This high surface area is essential for efficient oxygen uptake, as described by Fick's laws of diffusion. Water enters the mantle cavity, flows over the gills, and exits through the funnel. While the gills are the primary respiratory surface, the skin also plays a major role. At rest, the skin can account for approximately 41% of total oxygen absorption.

The octopus uses a unique respiratory pigment called hemocyanin to transport oxygen. Unlike the iron-rich hemoglobin found in vertebrates, hemocyanin is copper-rich. This pigment binds to oxygen in the gills and releases it into the tissues. During metabolic processes like the Krebs cycle, tissues use oxygen to break down glucose and release carbon dioxide. This carbon dioxide can combine with water to form carbonic acid, which lowers the blood pH. This change in pH is linked to the Bohr effect, which influences how oxygen is released from the blood. This system allows the octopus to maintain stable oxygen uptake even when environmental oxygen levels drop to 31.6% saturation.

Circulation is managed by a sophisticated three-heart system. One large, two-chambered systemic heart is responsible for pumping oxygenated blood to the rest of the body. Two smaller branchial hearts are located next to the gills. These branchial hearts pump deoxygenated blood through the gill capillaries to pick up oxygen. Once oxygenated, the blood returns to the systemic heart's atrium and then to its ventricle. The systemic heart then sends the blood through three aortae: the major dorsal aorta and two minor ones, the abdominal and gonadal aortae.

This system helps maintain the circulation required for their active lifestyles.

Movement and energy demands significantly impact the octopus's internal physiology. When crawling along the sea floor, an octopus increases its metabolic demand, requiring roughly 2.4 times more oxygen than when resting. The systemic heart compensates for this by increasing its stroke volume, which is the amount of blood pumped per beat. However, the octopus also uses a jet mechanism for swimming by creating high pressure in the mantle cavity. This jet propulsion is not a sustainable long-term method of travel. The high pressure required for jetting can constrict the vessels returning blood to the heart, causing circulation issues and oxygen debt.

Beyond their biology, the common octopus displays extraordinary cognitive abilities. They possess about 500 million neurons, a figure comparable to that of a dog. They can navigate mazes, recognize individual humans, and distinguish between different shapes, sizes, and brightness levels. They have even been observed learning to unscrew jars or raiding lobster traps. Some individuals create "gardens" by collecting shells, rocks, and algae. This unique behavior was even the inspiration for the 1969 Beatles song, "Octopus' Garden." Their intelligence and complexity make them a vital subject in marine biology and neurobiology.

Recent genetic research has also changed our understanding of the species. While once thought to be a single cosmopolitan species, scientists now recognize *Octopus vulgaris* as a species complex. This complex consists of six distinct members, each associated with specific geographic regions and continental coastlines. These members include *Octopus tetricus*, *Octopus americanus*, *Octopus aff. vulgaris*, *Octopus sinensis*, and *Octopus djinda*. Understanding these genetic distinctions helps scientists better protect and study the diverse populations of these remarkable cephalopods.