The Octopus Has Three Hearts (And Uses All of Them)

Meet the octopus, one of the most mind-bending, jaw-dropping creatures our planet has ever produced. With eight arms, a brain that wraps around its throat, and a personality that will genuinely surprise you, the octopus is proof that nature loves to show off. Whether you are a marine biologist, a curious kid, or someone who just stumbled across a cool fact online, you have come to exactly the right place, and you are going to love what you find here.

Why Octopuses Are So Extraordinary

• They have three hearts: two pump blood to the gills, one to the rest of the body
• Their blood is blue because it uses copper-based hemocyanin instead of iron-based hemoglobin
• They can change color in well under a second using chromatophores, and change skin texture too
• They have one brain, built as a ring around the esophagus, plus a nervous system running the length of every arm that lets each one act semi-independently
• They are widely considered the most intelligent invertebrates on Earth, capable of problem-solving, learning, and even play
• They have no skeleton and no shell, so they can force themselves through gaps far smaller than their body
• They can taste by touch, using two separate populations of cells in the suckers: one chemical, one mechanical
• Most species live only 1 to 2 years, making their remarkable intelligence and complex behaviors all the more astonishing

Three Hearts and Blue Blood: The Science

An octopus does not have one heart doing all the work. It has three. Two of these are called branchial hearts, and their sole job is to push blood through the gills, where it picks up oxygen from the surrounding water. The third, the systemic heart, then takes that freshly oxygenated blood and pumps it out to the rest of the body: the arms, the organs, the brain. It is a beautifully redundant system, built for an animal that needs reliable oxygen delivery across a body that can stretch, contort, and squeeze into impossibly tight spaces.

Here is where things get genuinely strange. When an octopus swims, the systemic heart actually stops beating. Not because the heart is squeezed, which is the usual explanation, but because nothing reaches it. Jet propulsion raises the pressure inside the mantle so far that the veins cannot push blood back against it, so the heart is left with nothing to pump. The result is that the octopus becomes temporarily oxygen-deprived in its core body, which is exhausting and uncomfortable. This is precisely why octopuses strongly prefer crawling along the seafloor to swimming. They are not being lazy. They are being physiologically sensible.

The blue blood is equally fascinating. Most vertebrates, including humans, use hemoglobin, an iron-based protein that binds oxygen and gives blood its red color. Octopuses use hemocyanin instead, a copper-based protein that turns blue when oxygenated. Hemocyanin is less efficient than hemoglobin, and the usual follow-up, that it makes up for this by working better in the cold, is the wrong way round. Cold makes hemocyanin grip oxygen too tightly to hand it over: at 0 degrees the Antarctic octopod Pareledone charcoti can release only about 16 percent of what it is carrying, rising to most of it at 10 degrees. Cold is a problem these animals compensate for, not an advantage they exploit, and how they manage it in the deep, chilly ocean waters where many octopus species live. Evolution did not make a mistake here. It made a very deliberate trade-off.

Masters of Disguise

The octopus's ability to change its appearance is not just impressive. It is one of the most sophisticated biological systems ever documented. The skin contains three types of specialized cells working in concert. Chromatophores are pigment-filled sacs that expand and contract under muscular control, allowing the octopus to flash colors across its skin in real time. Iridophores reflect light using microscopic protein structures, producing iridescent, metallic sheens that shift with viewing angle. Leucophores scatter light broadly, creating a white or pale background that makes other colors pop. Together, these three systems give the octopus a living, dynamic canvas.

But color is only half the story. Octopuses can also change the physical texture of their skin using structures called papillae, tiny bumps raised and flattened by concentric rings of muscle working as a muscular hydrostat. An octopus resting on a rocky reef can make its skin look like barnacle-covered stone. One sitting on coral can mimic the branching, lumpy texture of the coral itself.

Speed is the part usually exaggerated, including in earlier versions of this article. A measured chromatic pulse in Octopus laqueus takes about 0.55 seconds, and the fastest skin-pattern element documented anywhere in the literature is a cuttlefish hunting display at under a quarter of a second. Fast, then, but not the milliseconds you will often see quoted. The anatomy paper on papillae is careful to say they are built for rapid change without putting a number on it, so the widely repeated "one fifth of a second" figure comes from press coverage rather than from anyone's measurement. Nobody has published a time for a full color-plus-texture change.

Camouflage serves two purposes for the octopus: defense and predation. When hiding from a shark or moray eel, invisibility is survival. But when hunting crabs or small fish, the ability to approach undetected is equally valuable. The octopus is simultaneously prey and predator, and its disguise system serves both roles with equal elegance.

The Smartest Invertebrate on Earth

The octopus nervous system is unlike anything else in the animal kingdom. It has approximately 500 million neurons, which is comparable to a dog. But here is the twist: roughly two-thirds of those neurons are not in the central brain at all. They are distributed throughout the eight arms, with each arm containing its own cluster of nerve cells capable of processing information and executing movements independently. An octopus arm that has been severed from the body can still respond to stimuli and attempt to pass food toward where the mouth used to be. The arms are not just limbs. They are semi-autonomous agents.

They are not brains, though, and the "nine brains" line you have certainly read before, and which used to appear further up this page, is not anatomy. An octopus has one brain, a ring of fused ganglia around the esophagus holding roughly 45 to 50 million neurons, with the optic lobes accounting for a large share of the rest. What runs down each arm is an axial nerve cord and a chain of ganglia. That is a remarkable nervous system by any standard, and it does not need the upgrade.

This distributed intelligence shows up in behavior in remarkable ways. Octopuses in laboratory settings have learned to open containers sealed with rubber plugs, L-shaped puzzle boxes and screw-on caps. The childproof jar you see in every listicle, this one included until recently, appears in no peer-reviewed source. In one study all seven octopuses worked their way through a five-level container task, and the telling detail is what happened at each new level: performance dropped, then recovered quickly as they adapted.

They also recognize individual people. The study behind that is worth stating precisely, because it is usually reported as face recognition and it is not. Eight octopuses spent two weeks with one person who fed them and another who prodded them with a bristly stick, and afterwards responded differently to the two: different eyebar patterns, different arm reaching, different funnel direction, and in the four larger animals a different respiration rate. Nothing in the design separates the face from the body, the clothing or the way each person moved. What it shows is that an octopus can tell two humans apart and hold a grudge, which is arguably the better finding.

The most famous grudge was not at an aquarium. At the University of Otago in New Zealand, a laboratory octopus took a dislike to one member of staff for no reason anyone could identify and would deliver a jet of water down the back of her neck. The habit became expensive enough that the animal was released back to the wild. That is an anecdote reported by a philosopher of science rather than a controlled result, and it is worth enjoying on those terms.

Researchers have also documented play behavior in octopuses, which is significant because play is generally associated with animals that have rich inner lives. Individual octopuses in captivity have been shown to have distinct personalities: some are bold and exploratory, others are shy and cautious. Some are aggressive, others are gentle. The fact that octopus intelligence evolved completely independently from vertebrate intelligence (our last common ancestor was an early bilaterian animal more than half a billion years ago, too long ago and too soft-bodied to know much about) raises a profound question: if intelligence evolved twice, in such radically different forms, what does that tell us about the nature of mind itself?

A Life Lived Fast: The Octopus Lifecycle

For all their complexity, octopuses live extraordinarily brief lives. Most species survive for only one to two years. The giant Pacific octopus, the largest of all octopus species, lives perhaps three to five years, which makes it the long-lived exception rather than the rule. When you consider that an octopus must learn to hunt, master camouflage, solve problems, use tools, and navigate a complex ocean environment, all within a lifespan shorter than a typical house cat's kittenhood, the scale of what they accomplish becomes almost incomprehensible.

The hatchlings receive no parental guidance. They emerge as tiny, fully formed miniature octopuses and must immediately fend for themselves. There is no teaching, no mentorship, no learned tradition passed from parent to offspring. Everything an octopus knows, it figures out on its own, within its brief window of life. This makes the intelligence they develop even more striking. They are not standing on the shoulders of giants. They are building everything from scratch, every single generation.

The fact that octopus intelligence evolved independently from vertebrate intelligence, along a completely separate evolutionary path, is one of the most compelling arguments that intelligence is not a fluke. It is a solution that evolution finds again and again when the conditions are right. The octopus is living proof that the universe has more than one way to build a mind.

Octopuses in Culture and Science

Humans have been fascinated by octopuses for as long as we have been going to sea. The Kraken of Norse mythology, a sea monster large enough to drag entire ships beneath the waves, is generally traced to encounters with giant squid rather than octopuses, an identification that firmed up once Steenstrup described Architeuthis dux in 1853. Ancient Greek pottery and coins frequently depicted octopuses, and the creatures appear in Japanese art and folklore for centuries, most famously in Hokusai's woodblock prints. For most of human history, the octopus was a symbol of the deep's mystery and danger, something alien and unknowable lurking in the dark water below.

Today, octopuses are at the center of some of the most exciting research in neuroscience. Because their nervous system is so radically different from ours, studying how octopuses think, learn, and perceive the world gives scientists a unique window into the nature of cognition itself. Research into distributed cognition (how intelligence can emerge from a decentralized network of neurons rather than a single central processor) has implications not just for biology but for artificial intelligence and robotics. The octopus arm, which can solve problems without input from the central brain, is a model for soft robotics engineers designing flexible, adaptive machines.

Perhaps nothing shifted public perception of octopuses more dramatically than the 2020 Netflix documentary 'My Octopus Teacher,' in which filmmaker Craig Foster documents his year-long relationship with a wild octopus in a South African kelp forest. The film won an Academy Award and introduced millions of people to the idea that an octopus could have a personality, form a bond, and be genuinely missed when it was gone. The octopus went from monster to friend in the span of a single documentary, and the world has not looked at them the same way since.

Fun Curiosity: Octopuses are legendary escape artists: they have been known to slip out of tanks, cross the floor, and find their way back to the ocean. It is less a warning and more a testament to just how clever and determined these creatures are. Never underestimate an octopus with a plan.

Octopus intelligence sits in one body, but invertebrates have found other routes to a good decision. A honeybee swarm settles on a new home by voting, and the losing side gets head-butted into silence, which is a whole colony thinking without any single bee doing the thinking.

Three hearts, blue blood, a brain threaded around its own throat, and the audacity to escape from any container you put them in. Octopuses are, without question, one of the universe's greatest inventions, and the more you learn about them, the more the world feels like a wilder, more wonderful, more generous place than you ever imagined. They evolved their intelligence entirely on their own, along a path completely separate from ours, and yet here we are, recognizing something in them that feels almost familiar: curiosity, personality, cleverness, and a stubborn refusal to be underestimated. They live fast, love fiercely (in their own cephalopod way), and leave behind a generation of tiny, brilliant offspring who will figure everything out for themselves, just as their parents did. Every time a researcher discovers something new about octopuses, it does not just tell us more about them. It tells us something new about what life itself is capable of. And honestly, that is exactly the kind of feeling we are here for. The ocean is full of wonders, and the octopus is one of its very best.

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Two thirds of an octopus's neurons sit in its arms rather than its head, which the octopus Beastfile takes further.

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