Unsolved biology: 4 deep sea octopus mysteries

And then, in less than a second, the sand erupts. Eight arms unfurl. A body the size of a football materializes out of nowhere. A pair of eyes, eerily horizontal. And just as fast as it appeared, it is gone. It has dissolved back into the reef wall. This is an octopus. What is actually going on inside an octopus? What is it thinking? How does it see the world? It has been on this planet for roughly 300 million years, long before dinosaurs ever walked the Earth. It survived the mass extinction that wiped out nearly 96% of all marine species. It's a curiosity. A strange, slimy thing from the deep. In the last two decades, researchers have made discoveries about octopus biology and behavior that have genuinely shocked the scientific community. An animal that uses tools. An animal that has been observed playing, which is a behavior scientists once considered exclusive to warm-blooded vertebrates. But the octopus did not get smart the way we got smart. Evolution invented intelligence twice. Once in the vertebrate lineage, which eventually produced fish, reptiles, birds, mammals, and us. And once, completely independently, in the cephalopod lineage, which produced squid, cuttlefish, and the octopus. These two paths to intelligence share almost nothing in common. Our brains are centralized, protected inside a skull, built around a spinal cord. The octopus has no skull. It has no spine. It has no bones at all. Its brain is shaped like a donut, and its esophagus runs directly through the middle of it. Which means if an octopus tries to swallow something too large, it can literally give itself a brain injury. And yet, despite this completely alien architecture, the octopus is one of the most capable problem solvers on the planet. Meet the master of disguise. The mimic octopus is a sea creature with the amazing power to turn itself into other animals in seconds. It can shift its color, body form, and skin texture almost instantly. In nature, camouflage is often used to stay safe from predators. But it can also help hunters get close to their prey. This survival skill is a powerful result of evolution. Most forms of camouflage are about blending smoothly into the surroundings. But the mimic octopus does the opposite. Rather than hiding, it makes itself obvious, almost as if saying, come closer, I'm ready. Scientists have recorded these octopuses copying creatures ranging from mantis shrimp and seahorses to large crabs and starfish. Comment below and tell me what you think they are imitating. Here is how it works. Beneath the surface of an octopus's skin are three distinct layers of specialized cells, and each layer does something completely different. The outermost layer contains structures called chromatophores. Each chromatophore is essentially a tiny elastic sack filled with pigment, and it is connected directly to a set of muscles. When the brain sends a signal, those muscles pull the sack open, expanding it up to 500% of its resting size, and the color floods the skin. When the muscles relax, the sack snaps shut, and the color disappears. The octopus has millions of these cells, and it can control them with extraordinary precision, firing different combinations across different regions of its body to produce patterns of almost unlimited complexity. The second layer of cells, called iridophores, handles the problem of light. Iridophores do not contain pigment. Instead, they are built from stacks of ultra-thin plates that reflect and refract light the way a soap bubble does, producing iridescent blues, greens, and silvers that shift depending on the viewing angle. These cells allow the octopus to match not just the color of its surroundings, but the way light behaves on different surfaces. The third layer, leucophores, scatters white light across the skin to create contrast and brightness variation, filling in the gaps that the other two layers leave behind. And their visual system tells a fascinating story of its own. Octopuses have camera-style eyes with a lens, iris, and retina, following the same basic design found in vertebrate eyes. This stands as one of the clearest examples of convergent evolution. Two separate lineages, divided by 600 million years, reached almost the same answer to the challenge of forming images. But there is one major difference in how that design works. Vertebrate eyes contain a built-in flaw. The optic nerve runs through the retina, creating a blind spot where no photoreceptors are present. This happened because of the way our eyes formed during evolution, with the neural wiring ending up in front of the cells that detect light. Octopus eyes escaped this problem completely. Their photoreceptors face the incoming light source, and the neural wiring connects behind the retina. The result is a smooth visual field with no blind spot at all. It is a level of design that would make any human engineer jealous. They also have the power to detect polarized light, the directional movement of light waves, something humans cannot see. This ability helps them spot transparent prey such as jellyfish, notice contrast in places where colors barely differ, and perhaps even send signals through polarized skin patterns that most predators cannot detect. And that leads to what may be the most puzzling part of octopus vision. Strong evidence shows that they are functionally colorblind. The octopus is colorblind. Every piece of evidence we have suggests that octopus eyes contain only a single type of photoreceptor, which means they cannot distinguish between different wavelengths of light the way you and I do. They see the world in what is essentially a single channel of information. And yet, they produce color-matched camouflage that fools animals with full-color vision. For decades, this was one of the most maddening unsolved problems in cephalopod biology. The leading hypothesis right now involves those light-sensitive proteins we mentioned, called opsins. Researchers have found opsin proteins embedded directly in the skin cells of octopuses, completely separate from the eyes. The idea is that the skin itself may be able to sample the color of incoming light and use that information to calibrate the chromatophores, essentially seeing without seeing. The skin is not just a display. It may also be a sensor. Think about what that means for a moment. The octopus may be processing visual information across the entire surface of its body simultaneously, running a kind of distributed color-matching algorithm in real time, without any of it passing through conscious awareness the way our visual processing does. It is not thinking about what color to turn. It is just turning. Now, most octopuses use their camouflage system to blend in, to become invisible, to disappear. But one species took the whole thing in a completely different direction. The mimic octopus, discovered off the coast of Sulawesi in Indonesia in 1998, does not just blend into its background. It impersonates other animals. Specifically, it impersonates animals that predators are afraid of. When threatened, a mimic octopus can flatten its body and undulate its arms in a specific pattern to resemble a flatfish moving across the seafloor. It can tuck six of its arms into a burrow and extend the remaining two in opposite directions, holding them rigid and banded with black and white stripes, to mimic a banded sea snake, one of the most venomous animals in the ocean. It has also been observed mimicking lionfish by spreading its arms wide and holding them at angles that replicate the venomous spines of the lionfish's fins. It is the decision-making behind it. The mimic octopus appears to select which animal to impersonate based on the specific predator it is facing. When researchers observed it being approached by damselfish, which are particularly afraid of lionfish, the octopus chose the lionfish impersonation. When approached by other predators, it switched to different forms. That is not a reflex. That is a choice. It requires the octopus to recognize the predator, retrieve information about what that predator fears, select the appropriate performance, and execute it. All of this happening in an animal with no bones, no centralized brain structure anything like ours, and a total lifespan of roughly one to two years. There is one more layer to the camouflage system that most people do not know about, and it is the one that arguably makes the whole thing work. Color and light matching are impressive, but a predator with good eyesight can still detect an animal if its surface texture does not match the environment. A smooth patch of skin on a rough coral wall is going to stand out no matter how perfectly the colors match. The octopus solved this problem with structures called papillae. Papillae are small muscular projections embedded in the skin that can be raised or flattened on demand. When an octopus settles onto a rough surface, it raises its papillae to create a three-dimensional texture that matches the physical structure of what it is sitting on. When it moves to a smooth surface, it flattens them completely. The transition happens in milliseconds, and the octopus can produce dozens of distinct texture patterns, from fine grain to large irregular bumps, covering its entire body simultaneously. The combined effect of chromatophores, uridophores, leucophores, and papillae working together produces a camouflage system so complete that researchers have described watching an octopus disappear in front of their eyes as one of the most disorienting experiences in field biology. You are looking directly at it. You know it is there. And you still cannot see it. 500 million. That is roughly how many neurons an octopus has. For context, a honeybee has about 1 million. A mouse has around 70 million. A dog has roughly 530 million. So the octopus sits in the same general neighborhood as a dog in terms of raw neuron count, which is already surprising for an invertebrate. But what matters is where those neurons are. In your brain, and in the brain of every vertebrate on the planet, the overwhelming majority of neurons are concentrated in a single centralized structure inside the skull. Your arms do not think. Your legs do not make decisions. Your skin does not process information independently. Everything flows up to the brain, gets processed, and flows back down as instructions. The whole system is built around a central command structure. In an octopus, only about one-third of its neurons are in its central brain. The other two-thirds are distributed across its eight arms, with each arm containing its own dense network of roughly 50 million neurons. Each arm is, in a very real sense, a semi-autonomous processing unit. It can taste, touch, grip, explore, and make local decisions entirely on its own without waiting for instructions from the central brain. Researchers demonstrated this in a striking experiment. They severed an octopus arm from the body, which sounds brutal but was done under controlled conditions for scientific purposes. The detached arm continued to respond to stimuli for up to an hour after separation. It recoiled from unpleasant chemicals. It reached toward food. It executed complex coordinated movements involving multiple suckers working in sequence. The arm was behaving as though it were still part of a living animal, because, in a neurological sense, it still was. The central brain was gone, but the arm's own intelligence was intact. This raises a question that sounds philosophical but is actually a serious neuroscience problem. When an octopus reaches an arm into a dark crevice to search for prey, who is in charge of that arm? Is the central brain directing every movement? Or has it delegated the task to the arm itself, which is now operating on its own initiative while the central brain focuses on something else entirely? The evidence suggests it is the latter. The central brain appears to issue broad commands, something like, reach into that crevice and find food. And then the arm takes over, navigating the complex three-dimensional space of the crevice using its own sensory input and its own local processing, reporting back to the central brain only when it finds something relevant. The octopus is not one mind controlling eight arms. It may be closer to nine semi-independent minds operating in coordination. Here is something that sounds like a disadvantage but turns out to be one of the octopus's greatest assets. It has no bones. Not a single one. The only hard structure in its entire body is its beak, which is made of chitin, the same material as insect exoskeletons. For most animals, the skeleton is what makes precise movement possible. Your muscles pull against your bones to produce controlled, predictable motion. Without a skeleton, you would have no leverage, no structure, no way to generate directed force. You would be a bag of fluid. The octopus solved this problem in a completely different way. Instead of rigid levers, it uses what engineers call a muscular hydrostat, the same basic principle that makes your tongue work. A muscular hydrostat is a structure made entirely of muscle with no rigid internal support that achieves stiffness and direction by contracting muscles in specific combinations. When you stiffen one set of muscles along an arm while relaxing others, you create a temporary, rigid structure that can push or pull with considerable force. When you change which muscles are contracted, you change the shape and direction of the force. The result is an arm that can bend at any point along its length, in any direction, to any degree, simultaneously with any other movement. There is no joint limiting the range of motion. There is no bone that can break. The arm can squeeze through a gap the size of a coin, extend to full length to reach a distant object, coil around prey to grip it from multiple directions at once, and do all of these things at the same time in different arms. But controlling a structure like this is a computational nightmare. When you reach for a glass of water, your brain is solving a relatively constrained problem. Your arm has a limited number of joints, each with a limited range of motion. And your brain has learned, through years of experience, exactly which combination of muscle activations produces the movement you want. The math is complex, but bounded. An octopus arm has what mathematicians call infinite degrees of freedom. It can take on essentially any shape, which means the control problem is not just complex. It is theoretically unsolvable by a centralized brain working in real time. There are simply too many possible configurations to evaluate and select from fast enough to be useful. The solution the octopus evolved is to not solve the problem centrally at all. The arms solve it themselves. Each arm has internalized the physics of its own movement through a kind of embodied intelligence, a deep familiarity with its own mechanics that allows it to navigate complex physical situations without needing to consult the central brain for every micro-adjustment. The brain sets the goal. The arm figures out how to get there. The ocean is home to some of the most alien, intelligent, and visually stunning creatures on Earth. Here are the most beautiful octopus species in the world. The undisputed heavyweight champion of the cephalopod world, the giant Pacific octopus is as majestic as it is massive. Found across the North Pacific, these titans can reach lengths of 9.75 to 16 feet and weigh up to 110 pounds. They possess roughly 280 suckers on each arm, providing a grip that can hold on to almost anything. Small, vibrant, and incredibly dangerous, the blue-ringed octopus is the femme fatale of the ocean. Endemic to the Western Pacific and frequently spotted near Australia, they are famous for the iridescent blue circles that glow when they feel threatened. They have a surprisingly calm temperament and lack an ink sac, making them popular aquarium inhabitants. Despite their beauty, they produce tetrodotoxin, a potent neurotoxin also found in pufferfish. While they are not naturally aggressive, their bite is lethal. Often cited as the cutest inhabitant of the abyss, the Dumbo octopus gets its name from the ear-like fins positioned above its eyes, resembling the famous Disney elephant. These octopuses live at extreme depths of up to 13,000 feet. Unlike many of its cousins, the Dumbo octopus swallows its prey, like isopods and bristle worms, entirely whole. The blanket octopus is the definition of weird and wonderful. They exhibit extreme sexual dimorphism. While males are a tiny one inch long, females can stretch up to six feet. Females have large webs of flesh between their arms that look like a flowing blanket. If threatened, they can detach segments of these blankets to distract predators. They prefer the open ocean over the seafloor, drifting gracefully through the water column. If the giant Pacific is the largest, octopus Wolfie is its tiny, adorable counterpart. This is the smallest octopus species known to man. It measures only about one inch and weighs a mere one gram. They feature delicate papillae patterns and tiny suckers near the tips of their arms. They are typically found in shallow waters. The crown for the most beautiful octopus goes to the Caribbean reef octopus. This species is the ultimate expression of biological art, possessing a nearly limitless palette of colors and textures. It can instantaneously change its skin texture and color to match coral, sand, or rock. They are strictly nocturnal, emerging at night to hunt crustaceans across the vibrant reefs of the Caribbean. This is the question that makes philosophers and neuroscientists genuinely uncomfortable, because we do not have a good answer. We know that octopuses have no susceptors, the sensory cells that detect tissue damage and trigger pain responses. We know that when an octopus is injured, it changes its behavior in ways consistent with pain avoidance. It guards the injured area. It becomes less active. It shows reduced interest in food. These are the same behavioral signatures we use to infer pain in other animals. We also know that octopuses show something that looks very much like curiosity. When presented with a novel object, an octopus will approach it, examine it with its suckers, manipulate it, and return to it repeatedly over time. This exploratory behavior is not driven by hunger or threat. It appears to be driven by something more like interest, a motivation to gather information about the world for its own sake. There are documented cases of octopuses in laboratory settings squirting jets of water at researchers they appeared to dislike, repeatedly and specifically targeting the same individual while leaving others alone. There are cases of octopuses dismantling equipment in their tanks, not because the equipment was blocking access to food or shelter, but apparently because they found it interesting to take apart. One researcher described watching an octopus spend 45 minutes repeatedly dropping a pill bottle into the current created by its tank's water intake and catching it as it floated back, over and over again. By any reasonable definition of the word, that is play. And then there is the question of sleep. In 2021, researchers published a study showing that octopuses cycle through distinct sleep states, including one that involves rapid color changes across the skin. Flickering patterns that shift and pulse for several seconds before fading. The researchers proposed that this active sleep state may be analogous to REM sleep in mammals, the sleep stage associated with dreaming. If that interpretation is correct, and it is still a hypothesis, then the octopus may be the only invertebrate we know of that dreams. What does an octopus dream about? We have no idea. But the fact that we can ask that question seriously, about an animal this different from us, tells you something important about how far our understanding of consciousness and experience has come, and how much further it still needs to go. For most of the 20th century, the scientific consensus on octopus social behavior could be summarized in a single sentence. Octopuses are solitary animals that tolerate each other only long enough to mate, and sometimes not even then. Octopuses are territorial. They are cannibalistic under certain conditions. They spend most of their time alone in dens. When two octopuses encounter each other in the wild, the interaction often ends with one of them retreating, or worse. The solitary loner narrative made sense, and for decades, nobody seriously questioned it. Then, researchers started taking a much closer look, and what they found, nearly two miles below the ocean's surface, in one of the harshest environments on Earth, was that they were gathering together. In 2012, a team of marine biologists studying a population of gloomy octopuses, a species found off the coasts of Australia and New Zealand, discovered something that should not have existed according to the prevailing model. They found a site they eventually named Octlantis. It was a community, not a loose aggregation of animals that happened to be near the same food source, but a structured settlement of up to 15 individual octopuses living in close proximity, interacting regularly, and displaying a complex repertoire of social behaviors that nobody had predicted or prepared for. A new species nicknamed the Dorado octopus, but because it is also new, it has not yet been given an official name by scientists. The octopuses at Octlantis were communicating with each other using color and posture. Dark coloration, particularly around the eyes and mantle, was associated with aggressive intent and typically preceded physical confrontations. Pale coloration signaled submission and retreat. Specific postures, including what researchers described as standing tall, raising the body up on extended arms to appear larger, were used consistently in dominance interactions. These were not random behaviors. They were a social signaling system, a shared language of body and color that the animals were using to negotiate their relationships with each other. There were hierarchies. Certain individuals consistently dominated others. There were evictions, where a dominant octopus would physically remove a subordinate from a desirable den site. There were what appeared to be long-term social memories, with individual octopuses behaving differently towards specific neighbors based on the history of their previous interactions. None of this was supposed to exist in a solitary animal. The social complexity of octopuses does not stop at their interactions with each other. There is a behavior that has been documented in multiple locations across the Indo-Pacific that is so unexpected, it took researchers several years to accept it as real. Octopuses hunt cooperatively with fish. Not in the way that, say, wolves hunt cooperatively with each other, with a shared goal and coordinated strategy among members of the same species. This is something stranger, and in some ways more impressive. It is a cross-species hunting partnership between animals with completely different body plans, completely different sensory systems, and no shared evolutionary history of cooperation. Here is how it works. A grouper or a coral trout, both large predatory fish, will approach an octopus and perform a specific head-standing display, pointing its body vertically downward toward a crevice where prey is hiding. The octopus reads this signal, moves to the indicated location, and uses its flexible arms to probe into the crevice and flush out the hidden prey. The fish waits at the entrance. Whatever escapes the octopus gets caught by the fish. Both animals benefit. The octopus gains access to prey it might not have located on its own. The fish gains access to prey it could never reach inside a narrow crevice. The partnership works because each animal brings a capability the other lacks. What makes this genuinely astonishing from a cognitive standpoint is that the octopus has to understand what the fish is communicating. It has to interpret a signal from a completely different species, recognize it as meaningful, and respond appropriately. That requires a theory of mind, at least in a rudimentary sense. The octopus has to model the fish as an agent with intentions, understand that the head-standing display is a communicative act rather than random behavior, and act on that understanding. This is not something we expected to find in an invertebrate. It is barely something we expected to find outside of primates. Here is the part of the octopus story that is genuinely heartbreaking, and I think it is important not to skip over it. Most octopus species live for one to two years. Some of the smaller species live for only a few months. The giant Pacific octopus, the largest species in the world, with arms that can span up to four meters, lives for three to five years at most. These are among the shortest lifespans of any animal with comparable intelligence. And the end of an octopus's life is not peaceful. After mating, the male typically dies within a few weeks. The female lays her eggs, which can number in the tens of thousands depending on the species, and then she does something that is difficult to watch. She stops eating. She spends the entire incubation period, which can last several months, guarding the eggs, aerating them with her arms, cleaning them, protecting them from predators. She dedicates every remaining resource in her body to those eggs. And when they hatch, she dies. Every octopus that has ever lived has had to figure out the world entirely on its own, from scratch, with no parental guidance, no cultural transmission, no accumulated wisdom passed down from one generation to the next. And yet they are brilliant. Every single generation reinvents the wheel, and every single generation succeeds. Everything a human knows is built on a foundation of thousands of years of accumulated culture, language, education, and social transmission. We are not starting from zero. We are standing on the shoulders of every human who came before us. An octopus gets none of that. It hatches alone. It lives alone. It figures everything out alone. And in the space of one or two years, it becomes a sophisticated problem solver capable of tool use, social negotiation, cross-species communication, and possibly dreaming. If octopuses had longer lives, if they had the ability to accumulate and transmit knowledge across generations the way we do, there is a genuine scientific argument to be made that they would be the dominant intelligent life form on this planet. The fact that they are not is not a reflection of their cognitive capacity. It is a reflection of the evolutionary trade-offs that shaped their biology. Intelligence and longevity simply did not get packaged together in the cephalopod lineage the way they did in ours. That is not a failure of the octopus. It is a reminder of how contingent and arbitrary the path to any particular outcome in evolution really is. The octopus forces us to confront a question that is deeply uncomfortable for a species that has spent most of its history assuming it sits alone at the top of the cognitive hierarchy. What is intelligence, really? Is it the specific architecture we happen to have? The centralized vertebrate brain with its cortex and its hemispheres and its particular way of organizing information? Or is it something more fundamental, a capacity to model the world, to learn, to adapt, to solve problems, to experience, that can be implemented in radically different physical substrates? The octopus says it is the latter. Intelligence is not a structure. It is a function. And evolution will build it out of whatever materials are available as many times as it needs to because it works. That is not just a fact about octopuses. That is a fact about the nature of minds. And it means that as we look out into the universe and ask whether intelligence exists elsewhere, we should probably stop imagining creatures that think the way we think, with brains that look like ours, in bodies that move like ours. The universe has had 13.8 billion years to run the same experiment that produced the octopus. The results, whatever they are, are almost certainly stranger and more wonderful than anything we are currently prepared to imagine. So let us bring it all together. The octopus has a camouflage system so sophisticated that its skin may be able to see color independently of its eyes, producing real-time disguises that fool animals with full-color vision despite the octopus itself being colorblind. It has a nervous system so radically distributed that each of its eight arms operates as a semi-autonomous intelligence, capable of independent decision-making, sensation, and complex movement without instruction from the central brain. It has a social life far richer than we ever suspected, complete with communication systems, dominance hierarchies, long-term social memories, and cross-species hunting partnerships with fish. It plays. It may dream. It solves problems no one taught it to solve in a lifespan shorter than most of our attention spans. And it did all of this by taking a completely different path than the one that produced us. If you have ever looked at the ocean and felt like there was something vast and unknowable out there, something that operates by rules you do not fully understand, you were right. And it has eight arms. If this video changed the way you think about intelligence or about what is going on beneath the surface of the ocean, let me know in the comments. I want to know which part surprised you most. Was it the skin that might be able to see? The arms that think for themselves? The social lives nobody predicted? Or the fact that an animal this extraordinary lives for barely two years and still manages to figure everything out from scratch? Drop it below. I read everything. And if you want to dive even deeper into the science of animal intelligence, I made a video exploring the animals that break the rules of death. That video is linked on your screen right now. I'll see you there.