Octopuses: Learn 11 Awe-Inspiring Features of The Eight-Limbed Marine Animal – Part 2

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Updated on: Educator Review By: Michelle Connolly

So we are still going on with our journey deep down in the ocean, tracking and studying the mighty octopus. In Part One, we have demonstrated some interesting information about its fantastic body, which turned out to be nothing like anything else in the animal world.

We started by learning about the octopus’s entire body structure, headquartered by a head, or a mantle like scientists call it, that comprises all the vital organs. We understood why the octopus has blue blood and how this forced the evolution of three hearts. After that, we studied the animal’s eight limbs as well as its hundreds of suckers.

In this article, we are going to demonstrate six more majestic superpowers this extraordinary animal possesses.

Pink octopus in cartoon design

So let’s hop into it.

1. Octopuses have nine brains.

Our brains consist of nerve cells known as neurons. These neurons are the brain’s basic unit, which scientists call information messengers. They send information between the different parts of the brain using electrical signals and send instructions to the different body parts.

In other words, the brain and neurons act like a leader and assistants. The brain controls the entire body by using the neurons to tell the different organs what to do.

In humans, neurons are found in the brain and spinal cord. In mighty octopuses, only 40% of neurons are located in the brain, while the remaining 60% are found in the eight limbs. That means the neurons in each arm control it independently from the central brain. As a result, each arm can be doing a different function simultaneously.

That means octopuses have nine brains. While the main one is located in the mantle, the other eight tiny ones are found in the arms.

This is a great feature, for it allows the main brain to focus on the most important things. While the arms look for food, open shells, taste what is inside them, or touch and grab objects, the main brain can be on the watch for predators. So if any approaches, the octopus can react accordingly to escape it.

2. They ink when they are threatened.

While the octopus itself feeds on small fish, snails, crabs, clams, and sometimes other octopus species, a behaviour known as cannibalism. Some marine animals feed on octopuses as well, such as seals, sharks, whales, sea otters, moray eels, and even some bird species. Therefore, octopuses are prey animals.

To protect themselves from predators, octopuses have multiple defence mechanisms, the first of which is known as inking. When they feel threatened, octopuses release ink to confuse their attacker and run away.

So how does this happen?

The digestive gland is one of the many organs found in the octopus’s mantle. In addition to generating saliva, the digestive gland produces ink and stores it in a sac located below it. As the ink has a high level of melanin, the pigment that gives the skin, hair, and iris a black colour, it, the ink, also turns out black. 

When the octopus is approached by one of the many predators that feed on it, or when it feels threatened in general, it desperately tries to defend itself by releasing ink. This ink irritates the predator’s eyes and temporarily blinds it, giving the octopus time to run away. The ink was also found to momentarily paralyse the predator’s sense of smell, so it fails to locate the octopus.

On some rare occasions, the octopus may feel more courageous than threatened. So it releases the ink to scare the predator. Consequently, instead of the octopus running away, it is the predator that is forced to escape.

Interestingly, this inking technique also helps save other marine animals that may be around. Once they see the black ink, they quickly understand a predator is nearby so they, too, run away.

That said, the octopus’s ink happens to be irritating to the octopus itself too. That is why the octopus pulls itself back quickly after releasing it because if it does not, the ink can badly affect it.

The octopus’s ink is indeed not poisonous, but this mighty animal does have the ability to release venom.

3. They are venomous.

Well, that is true. Octopuses are venomous; all 300 octopuses species are. This is another defence mechanism these creatures use to defend themselves and escape predation. What is different here is that octopuses also release venom to kill prey while hunting.

Most, if not all, animals and birds have their mouths or beaks, typically under the nose on their heads. But as we learned, octopuses are different. They have their beaks, which look pretty much like those of parrots, right at the intersection point of all eight limbs, from below. Those beaks are sharp and strong enough to break hard shells and bite animals.

As octopuses use their beaks to bite their enemies, they release venom to kill them. While the bite itself may not hurt a lot, most animals feel tremendous pain due to the venom.

Interestingly, the venom is produced by the same digestive gland, which stimulates saliva as well as ink. That is why releasing the venom after the bite is so easy.

4. They can change their skin colour.

Like the chameleon lizard, octopuses are able to change their skin colour instantly if they feel threatened, another unique defence mechanism known as camouflage which octopuses use to escape danger.

Like producing ink and venom, camouflage is not limited to a few species of octopuses. In fact, all 300 species, as well as the other members of the family, like squids and cuttlefish, are able to change their colour.

So how do they do that?

Under their skin, octopuses have cells called chromatophores. These are responsible for changing the skin colour. They have small sacs of differently-coloured pigments, ranging from black, grey, and brown to orange, red, yellow and blue.

These sacs are just as elastic as balloons. When they expand, the colour appears, but when they contract, it disappears. This is like turning colours on and off by expanding or contracting.

Octopuses have 20 million of these chromatophores. Now you can imagine how efficient octopuses are in changing their skin colour.

But these are not the only cells that help change skin colour. Octopuses have other cells under the skin known as iridophores. Iridophores can reflect the light to create a luminous effect. This typically happens with the green, silver, blue or gold colours. Interestingly, these luminous colours change when seen from a different angle.

In addition to changing colours, the octopuses can change its skin pattern and texture. If it has stripes, it turns them into rings. If the skin is soft, it can make it have a rough texture to resemble a coral or rock so predators do not recognise it.

octopus LearningMole
Blue octopus on white background

5. They have horizontal pupils.

Besides the large mantle, the downward-facing beak, the eight limbs, the hundreds of suckers, the three hearts and nine brains, octopuses are also characterised by their large deep eyes.

Humans have small eyes compared to large bodies. Their pupils are circular. According to the amount of light, the human pupils get bigger or smaller while maintaining their circular shape. On the other hand, cats have circular pupils that turn vertical in bright places.

But, again, octopuses are different. Their eyes are quite large in relation to their bodies. Their pupils, which are what we are concerned about here, are circular in the dark. But if its bright around, they become dumbbell-shaped and turn horizontal.

As we mentioned in Part One, octopuses are nothing but pure muscles. Just like how many different muscles control suckers, each eye is controlled by seven muscles, each of which is connected to a different nerve.

This complicated structure allows each eye to move independently from the other. Each eye can move up and down and zoom in and out, just like a camera lens, to adjust the vision and provide the octopus with a full vision on both sides.

Despite that, the octopus’s eyes turned out to have some deficiencies. For instance, octopuses were found to be colour-blind. They have a single receptor in their eyes, which limits the colours they see to black and white only. That said, their eyes can still detect (but not see) other colours and use them to camouflage.

Additionally, octopuses are short-sighted. This means they can see nearby things but not those far away. The maximum distance at which octopuses can see clearly is only 2.5 metres. If an object is positioned further than that, they will not see it with accuracy.

6. Reproduction kills them.

Everything we mentioned so far about the octopus’s body in Part One, as well as this part, helps it survive and flourish in their natural habitat. We have seen how octopuses release ink and venom to escape death, how their three hearts sustain their active lifestyle, and how their nine brains multitask.

But it is also this marvellous body that kills the octopus.

To understand how this happens, we must go over the octopus’s reproductive cycle, which is quite complicated since this animal’s reproductive system, for both males and females, is found in its mantle. But let’s try to simplify things anyways.

To create a baby octopus, a sperm from the male must fertilise an egg from the female. When it is time to mate, the male octopus moves the sperms from its reproductive system in the mantle down to one of its eight arms. Then, it approaches the female and injects its arm through an opening in the female’s mantle. Therefore, sperms move to the female reproductive system and fertilise the eggs.

In one breeding season, up to 70,000 eggs are fertilised. After around a month or 40 days, the female lays the eggs in a safe place, mostly around rocks, and takes care of them for a certain period of time. This period is different from one species to another. For the giant Pacific octopus, for instance, the female takes care of her eggs for about five months before they hatch.

After mating, both males and females experience ageing, a phenomenon known as senescence. Their bodies start to deteriorate. They stop eating, which weakens their bodies even more, making them easy prey to any predator crossing by. Males experience this phase right after mating. If they are not eaten by predators, it usually takes males a few weeks to several months to die.

On the other hand, females hold themselves together until they lay the eggs. Then deterioration starts. They stop eating, and their cells, as well as organs, break down one after the other, and before they know it, they die.

As a result, both males and females reproduce only once.

Octopuses were found to stop eating because the optic gland, which is an organ in the mantle, prevents the digestive glands from working during reproduction. Consequently, they die of starvation.

Scientists could know that by experimenting. After one female octopus laid her thousands of fertilised eggs, scientists removed the optic glands from her mantle, and the result was terrific. The female continued to eat and did not starve. But this also had an awful drawback.

Since the optic glands are responsible for the reproductive behaviour, their removal prevented the female from incubating her eggs or protecting them. This, in return, destined most of them to death before hatching. So whether the optic glands are left or removed, only the mother or her eggs will live. Without human intervention, nature has decided it is the mother that should die.

Here one might ask, why is nature so cruel? Why cannot both parents, as well as their eggs, live?

Well, it surely is cruel. But it was made this way to keep a balanced ecosystem. Since females lay thousands of eggs, parents dying after mating help inhibit overpopulation!

This applies to all octopus species except for one, which is the larger Pacific striped octopus. Although it does not live over two years, neither the males nor females of this species die after reproduction. Therefore, they can breed multiple times during their lifetime.

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Cute octopus cartoon character


So here we get to the end of Part Two, where we continued to study some fantastic things about the mighty eight-limbed marine animal, the octopus.

Besides its three hearts and blue blood, we learned that the octopus has nine brains, one main brain found in the mantle and eight tiny ones found in the limbs. Thanks to incorporating over 60% of the neurons, the limbs are able to ‘think’ on their own and perform completely different tasks pretty independently from one another.

Then, we discussed three stunning defence mechanisms the octopus uses to protect itself from predators. Whenever it feels threatened, the octopus can either release black ink into the water to confuse its attacker or bite it and inject its deadly venom inside its body. But if the octopus is too scared to do any of these, it will just camouflage, blend in the environment and pretend it is not there.

After that, we studied the octopus’s large eyes and its dumbbell-shaped, horizontal pupils. We then finished with the animal’s reproductive cycle and how it kills both males and females to help maintain a balanced ecosystem.

We hope you enjoyed learning more things about octopuses as much as we loved teaching you about them. Now that you know how majestic these marine animals are, you can move on to learn about one of their predators, the whale, or explore how chameleons also change their skin colour and pattern. 

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