The clever octopus is full mystery and surprise. Some of their cognitive abilities are eerily human-like, yet their blue blood, multiple hearts and remarkable nervous system are more reminiscent of alien life. There's evidence that these highly intelligent animals can recognize and have preferences for individual humans, use tools, identify visual patterns and solve problems—surprisingly complex behaviors for an invertebrate closely related to a clam. The more we learn about octopuses, the more questions we seem to have—and the more we seek to understand.
Masters of Disguise and Escape
The wily octopus has a variety of remarkable escape tools in its arsenal.
Click on the circles to see how an octopus's chromatophores expand and contract. →
Of the octopus's many skills, the most visually stunning is its ability to instantaneously shift the color and texture of its skin to become virtually invisible to predators—or to wait undetected for passing prey. A complex network of nerves commands the muscles inside pigment-containing cells, called chromatophores, to expand or contract, making the color inside more or less visible. Texture manipulation involves controlling the size of projections on the skin—called papillae—to create bumps, ridges and horns, allowing this incredible animal to seamlessly blend in with coral, rocks and other elements of the sea floor.
Their soft, boneless body allows them to shape-shift, squeezing through any space large enough to fit their small, sharp beak, which is made of a substance called chitin. The largest species—the giant Pacific octopus—can weigh up to 50 pounds, and squeeze through an opening only a few inches wide.
Octopuses tend to crawl along the ocean floor using their powerful eight arms, but they have a much more effective form of locomotion when they need to move quickly: jet propulsion. By rapidly drawing water into and out of a funnel-like structure, called a siphon, the octopus can quickly jet through the ocean and away from predators.
If you think you don't have anything in common with these blue-blooded, bulbous mollusks, think again.
Hover for a closer look at an octopus's circulatory system. →
Like humans, octopuses have closed circulatory systems, meaning that closed vessels or tubes transport blood throughout their body. Two of their three hearts, the branchial hearts, pump blood through the octopus's gills, where it releases carbon dioxide and absorbs vital oxygen—much like the right side of our heart passes blood through our lungs. The blood then enters the main, or systemic, heart, which circulates the newly oxygenated blood throughout the body, like the left side of human hearts. Both humans and octopuses have a protein in their blood that carries oxygen; hemoglobin for humans, and a copper-rich protein called haemocyanin in octopus blood, which gives it a distinctive blue color.
The parallels between humans and octopuses don't end there—our brains produce similar electrical patterns, feature complex folded lobes and are capable of short- and long-term memory. Even the physical structure of our eyes is nearly identical to that of an octopus, except for our "blind spot" where the optic nerve passes through the retina. Since an octopus's optic nerve passes behind the retina, its eyes have no such blind spot.
Colorblind and Color-Changing
Yet another mystifying aspect of the octopus: these cephalopods are technically colorblind, but they're masters of color camouflage. So how do they distinguish color? The shape of their pupils may play a part.
An octopus's eight sucker-lined arms—not tentacles!—have a variety of fascinating functions.
Hover to watch an octopus sucker expand. →
The octopus's arms contain two-thirds of all its neurons, enabling their impressive limbs to taste, feel and control basic movements independently of its brain. This system allows the octopus's arms to independently do some of the "thinking," lightening the cognitive burden on the central brain and allowing for multi-tasking. Curious by nature, octopuses tend to explore with their eight powerful arms, which they wrap around prey and objects to taste, tug closer and explore using their impressive suckers.
Inside each sucker is a cup-like chamber, called an acetabulum. When the acetabulum expands, the pressure inside the sucker decreases. The higher pressure outside the sucker pushes against it, creating the octopus's signature mighty grip.
An octopus's rimmed suckers are the key to this cephalopod's iron-strong grip, which it uses to pry open the hard shells of its prey. The largest species, the giant Pacific octopus, has more than 2,000 of these powerful suckers, which can haul up to 700 pounds.