So, the octopus. It’s one of nature’s most incredible creatures, but how much do you know about it?
You probably think they’ve got eight arms, right? But what else?
There are so many things that make octopuses awesome. For example, do you know how many brains does an octopus have?
You might be surprised to learn that octopuses have nine brains!
We’re going to delve into this and find out WHY does an octopus have nine brains.
Then we will look at more fascinating octopus facts than they have arms or brains!
How Many Brains Does an Octopus Have?
The headline answer that you’ll usually see to “how many brains does an octopus have” is nine. Sounds impressive, right?
However, not all of the octopus nine brains are the same.
Accurately, we can say that the multiple brains in an octopus are made up of a main, central brain situated between the octopus’s eyes and eight mini-brains, each found at the base of the octopus’s arms.
Together these multiple brains give the octopus extraordinary intelligence and lightning-fast reactions.
To understand all this and how it makes the octopus so clever, let’s take a look at how the nervous system and senses work, starting with what the central brain controls.
One Central Brain
As you’d probably expect, the central brain sits in the octopus’s head. So far, so normal!
Somewhat less ordinary is the shape of the central brain. It’s housed in a cartilaginous capsule and has a doughnut shape that runs around the octopus esophagus.
The central brain is divided into four functional areas:
Intermediate Motor Centers – Controls coordinated movement of the arms. The lower motor centers, which contain the neurons that control actual muscle contractions and motion, are located in each leg’s small brain (more on that below).
Higher Motor Centers – Control movements that involve the octopus’s entire body.
Receptor Analyzers – These interpret inputs from the octopus’s sensory receptors, including the visual information and touch
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Memory Centers – The memory system is situated in the superior frontal, vertical, and sub-vertical lobes and, as we shall see later, give the octopus quite impressive recollection.
A typical octopus species, such as the common octopus (Octopus vulgaris), possesses about 500 million neurons, the messengers that transmit the nervous system’s information.
Only about 180 million of these are in the central brain itself. The remaining 320 million are divided into each small brain found in the eight arms.
Eight Mini Brains
The so-called mini-brain at the base of each arm contains the lower motor centers. These nerve cords can make movements and complex reflex actions without input from the central brain.
The high concentration of neurons means that each arm can act independently from the others enabling them to react extremely quickly to sensory inputs, including touch and taste.
The Benefits of Having Mini-Brains
Having nine brains in total might seem greedy, but they give the octopus many benefits.
Octopuses don’t have a fixed map of precisely what their arms and bodies are doing because they constantly adapt to their environment.
The mini-brains in each arm removes the responsibility of reacting to, for example, touch from the central brain, leaving it to concentrate on more complicated things like memory.
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Giving each arm its own brain means that fine movements to explore objects and make reactions to threats are made as quickly as possible without communicating with the central brain.
An octopus even possesses the fantastic ability to deliberately sever one of its legs. This might be useful if the octopus is under attack and needs to create a distraction.
The chopped-off leg can use its mini-brain to wriggle off (they can continue to move for about an hour), perhaps giving the octopus enough time to make its escape!
An octopus’s nervous system has evolved from ancestors that split into mollusks and vertebrates over 600 million years ago.
Vertebrates have a nervous system with a spinal cord of nerves and a brain at one end.
Invertebrates have interconnected neurons clustered together in knots around their body.
Octopuses and other cephalopods evolved with more complex neuron knots, called ganglia, and some of these concentrated into a central brain.
Others formed the mini-brains, which directly control each arm.
The eight mini-brains even have a neural ring so that they can talk to each other and coordinate without having to communicate with the central brain.
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The central brain is responsible for working out what the octopus needs, and it will communicate this to the arm mini-brains so they can use their sensory information to get the job done.
The mini-brain in each of the arms determines how it needs to move and will respond to its senses. Each arm will process information and send back what’s necessary to the central brain.
So there you have it. Octopuses have nine brains!
The development of this devolved nervous system is one of the reasons that the octopus is so intelligent for its size.
It’s also played a significant part in helping the octopus stay safe when facing predators.
Having eight legs with a nervous system that can react independently with incredible speed is handy when something is trying to eat you!
How Many Hearts Does an Octopus Have?
We’ve discovered that an octopus has nine brains, but how many hearts does an octopus have?
Well, in another feat of the strange, an octopus has three hearts!
Why do octopus have three hearts? Well, it’s to do with them having evolved in cold water or where there was less oxygen available.
Because of this and their particular type of blood (see below), an octopus needs to pump its blood at high pressure to get oxygen where it’s needed, and this requires more than one heart.
Of these three hearts, the octopus has one main one (a systemic heart) and two smaller ones (branchial or gill hearts).
The larger heart circulates blood that is oxygenated to the organs and around the body.
Meanwhile, the two smaller hearts pump blood to the gills for oxygen exchange.
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The larger of the octopus hearts can only pump blood to the rest of the octopus while the animal isn’t swimming.
The lack of oxygenated blood to the rest of the body means that these octopuses can only swim for short periods before needing to stop or crawl.
What Color Is Octopus Blood?
The three hearts of an octopus are pumping blood that is blue when it’s oxygenated.
By the way, if you’re wondering, are octopus warm-blooded? The answer is no. Octopuses are cold-blooded animals, which is connected to why the octopus has blue blood.
Why is Octopus Blood Blue?
Octopus blue blood has evolved to transport oxygen efficiently in cold ocean environments.
The blue blood contains a copper-rich protein called hemocyanin which is more efficient at transporting oxygen in cold water with low oxygen levels than more usual hemoglobin.
The hemocyanin gives the oxygenated blood a blue color and is very dense.
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Remember the three hearts? Thick blue blood is one of the reasons why, as it needs a high-pressure heart system to pump it around the body.
How Many Suckers Does an Octopus Have?
Each of the octopus’s eight arms is covered in suckers that can smell and taste as well as grip and squeeze.
The total number of suckers that each octopus has is species-dependent. Typically the larger the octopus, the more suckers.
Most octopuses have a double row of suckers on each arm from their mouth. The closer to the mouth, the bigger the sucker.
The most enormous octopus, the giant Pacific octopus, has about 280 suckers on each arm, and they can measure as large as 6.3 centimeters (2.5 inches) in diameter.
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Each sucker can have approximately 10,000 neurons that the octopus uses in chemo-receptors to investigate its environment by touch.
Scientists have even studied octopus suckers to try and recreate their ability to attach to a substrate in wet conditions, including rough surfaces.
How Many Tentacles Does an Octopus Have?
The word octopus comes from the Greek “Oktopus,” which means “eight footed,” but you’ll usually hear them called legs, arms, or sometimes tentacles.
What Is the Difference Between an Arm and a Tentacle?
A cephalopod tentacle (like those on a squid) comes in pairs, is retractable, and only has suckers around its tips.
Meanwhile, an arm (as found on an octopus) is generally shorter, stronger, and has suckers on its entire length.
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So, octopuses do not have tentacles. They have arms.
Scientists have determined that most octopuses have two legs and six arms.
This is because the octopus favors two of its arms specifically for walking along the seabed, while the other six are used for feeding and interacting with objects.
10 Other Fun Facts About the Octopus
Multiple brains, three hearts, blue, copper-based blood, thousands of suckers, and eight arms. That’s just the beginning of the fascinating world of these amazing creatures.
Let’s take a look at some more fantastic octopus facts.
Octopus Don’t Have Ears
You may think that the answer to “Do octopus have ears?” is yes because you’ve heard about the incredible dumbo octopus.
However, no matter how it may look, even this octopus doesn’t have ears. They’re actually two large fins, one on either side of the mantle, that just look a bit like ears.
Octopuses don’t have any traditional organs for hearing. However, scientists have investigated whether these marine creatures can detect sound in other ways.
The octopus has two organs attached to its central brain called statocysts. These are used by the octopus for balance and to keep the octopus properly oriented relative to gravity.
It’s also believed that the statocysts may give the octopus some ability to detect sounds in a simple way, and studies have shown the octopus reacting to sounds between 400 Hz and 1000 Hz.
So while octopuses can’t hear in a traditional sense, they can detect some sound vibrations in the water.
Octopuses Have Only One Stomach!
Having heard about multiple brains and hearts, you might think that an octopus will also have many stomachs. Actually, this is not the case!
How Many Stomachs Does an Octopus Have?
The octopus has one stomach, but its digestive tract is still pretty complicated.
When an octopus grabs food in its arms, it delivers it the buccal mass to begin digestion.
The buccal mass comprises the mouth with its sharp two-part beak, the salivary glands, and the radula, which is like a tongue albeit covered in tiny teeth.
The food is broken into small pieces and forced down the esophagus into the gastrointestinal tract.
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The tract contains a large crop used to store food before it enters the stomach. The crop is very large compared to the stomach, meaning the octopus can eat surprisingly large prey.
Enzymes in the crop begin digestion while the food is held, and when it enters the stomach, the food is ground down into a sludge before it moves to the caecum pouch for absorption.
Liver cells break the food down further and absorb fluids in the digestive gland, and finally, the remaining waste left in the intestine becomes fecal ropes to be excreted.
Octopuses Have Incredible Intelligence in Their Nine Brains
Would it surprise you to hear that an octopus is as intelligent, or maybe even smarter than your cat or dog?
It might not be the largest if you’re comparing the octopus brain size with other animals. However, you must remember that these animals have nine brains, meaning that the total brain-to-body weight ratio is the highest of all the invertebrates and larger than many vertebrates.
The common octopus (Octopus vulgaris) has approximately 500 million neurons, about the same as a dog. Like a dog, an octopus can navigate, solve problems, and possesses short and long-term memory.
If you want another comparison, an octopus has more neurons in just one of its arms mini-brains than a frog has in its entire body!
You’ve probably never heard of a frog completing complicated tasks. On the other hand, scientists have tested octopuses and had them navigating mazes, unscrewing jars for food, untying knots, and completing puzzles to escape from enclosed spaces.
Octopuses Can Use Tools
Another demonstration of the high levels of octopus intelligence is their ability to use tools.
Usually, this remarkable intelligence is reserved for highly evolved vertebrates, including monkeys, apes, and dolphins.
Lab experiments have seen the octopus use tools to get to food rewards, and in the wild, they use them too.
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After finding a suitable den, octopuses often collect stones and use them to make shields.
The octopus will use its eight arms from inside the den to pull in stones and pieces of coral to barricade itself in completely.
Sometimes this collection of underwater debris has been referred to as an octopus’s garden. Perhaps you know The Beatles song that was inspired by this behavior?
Veined octopus (Amphioctopus marginatus) have been seen in Indonesia collecting coconut shells from the seabed.
The octopus would clean the shells up and assemble them on the sea floor to build a protective shell house in a preferred location.
It’s even been seen that the octopus picks up its shells one by one and moves them to a new place, perhaps when the neighbors are being annoying!
Octopuses Have the Memory to Recognise and Respond To Different People
The optic lobe, which is the area of the brain focused on vision, is especially large in an octopus, so it’s believed that their vision is important and well developed.
Scientists have discovered that octopuses can recognize human faces and even remember them.
In an amusing story from the University of Otago in New Zealand, an octopus, for reasons unknown, decided it didn’t like a particular member of staff.
Every time the person walked past the octopus tank, no matter what they wore, so long as they didn’t cover their face, the octopus would squirt a jet of water at them.
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The Seattle Aquarium devised a test to prove if the octopus indeed remembered unhappy events. While both were wearing identical clothes, one team member fed the octopuses for two weeks while another touched them with a bristle stick.
In the end, the octopus’s behavior was noticeably different to the two keepers.
So if you do something to annoy an octopus, they will remember!
Octopus Mums Make the Ultimate Sacrifice for Their Kids
Once they’ve laid their eggs, the female octopus will tend them continually.
The female keeps an eye out for predators and constantly wafts oxygenated water over the eggs to keep them healthy.
It can take up to seven months for the eggs to hatch, and this constant work takes a massive toll on the female, who cannot eat during the whole time.
The female will eventually weaken, and her body will degenerate as it begins a process of self-cannibalism to attempt to stay alive as long as possible.
Once the eggs hatch, the female octopuses die, usually from an opportunistic predator taking advantage of her weakened state.
Octopus Have Toxic Ink
You probably already know that octopuses have black ink, which they can squirt at predators to create a cloud of confusion, allowing them to make a getaway.
The ink is stored in large sacs and is squirted out of the octopus siphons at great speed and simultaneously propels the animal in the opposite direction.
Octopus ink is made from melanin and mucus, which stops the ink cloud from dispersing too quickly.
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It also contains venom to give a nasty surprise to would-be attackers. It’s thought that the toxic ink affects the ability of octopus predators like the moray eel to smell or sense the octopus.
With the aggressor’s senses numbed by the toxic ink, the octopus is at a great advantage and can escape quickly.
The Giant Pacific Octopus is the Biggest, By Far
The giant Pacific octopus (Enteroctopus dofleini) is by far the largest octopus.
The Guinness Book of Records says that “The biggest giant Pacific octopus specimen on record sported a tentacle span of 9.6 m, and an estimated weight of 272 kg.”
As well as having the most suckers of any octopus, the giant Pacific octopus is also the strongest.
The biggest suckers of the giant Pacific octopus can lift individual weights of 15 kilograms (35 pounds).
Some Octopuses Live in Communes
Most octopus live solo lives except when the time comes for reproduction.
However, in 2012 scientists in Australia discovered that the gloomy octopus (Octopus tetricus) builds communes with other octopuses.
Groups of up to 15 dens were found together underneath rocky outcrops on the sea floor, covered in discarded shells from clams and scallops after a feast.
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The scientists named the unexpected mini-city “Octlantis,” and just like human cities, noticed occasional arguments between neighbors.
It isn’t known for sure if the octopus has chosen to live together or if they’ve been forced to by the lack of local shelters.
Either way, it’s a fascinating behavior to observe.
There’s a Seven-Arm Octopus (Kinda)
Finally, to close our octopus facts, we can confirm that there is a seven-arm octopus (Haliphron atlanticus).
No, this isn’t an octopus that has accidentally lost a leg. It’s an octopus that appears to have only seven arms.
The key word is “appears.” The male octopus has a coiled up hectocotylus, the unique arm that is used as a penis for reproduction.
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This arm is kept coiled in a sac underneath the octopus eye, giving it the appearance that the male octopus species only has seven arms.
In fact, strictly speaking, the male seven-arm has eight arms. It’s just that one is kept out of view!
There are few more amazing creatures in the animal kingdom than the octopus.
As we’ve looked at how many brains does an octopus have (Nine!), we’ve also learned that they have three hearts, blue blood, and thousands of suckers, amongst other cool octopus facts.
Just remember, those are eight arms and not eight tentacles!
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British-born Dan has been a scuba instructor and guide in Egypt's Red Sea since 2010.
Dan loves inspiring safe, fun, and environmentally responsible diving and particularly enjoys the opportunity to dive with sharks or investigate local shipwrecks.
When not spending time underwater, Dan can usually be found biking and hiking in Sharm's desert surroundings.