But we've been ignoring an equally as incredible aspect of their camo abilities: 3-D morphing.
Yes, they can squeeze their bodies to fit through just about any opening or contort their arms to resemble a snake, fish or plant. But the can also rapidly unleash a textural disguise.
Under their skin, these animals have a network of finely controlled muscles that can create fine bumps, high ridges or even spikey horns that they can deploy to match their surroundings. Such shifts can help them hide from hunters—as well as their own potential prey.
Despite centuries of observation, however, we humans know little about how octopuses accomplish this unusual feat.
To peer beyond the octopus's skin, researchers at Woods Hole used scanning electron and brightfield microscopes to look at the muscles below. They published their analysis of four different species of octopus (and two species of cuttlefish) in December in the Journal of Morphology.
These strange structures are composed of muscular hydrostats—similar to the octopus's arms and to our tongues—which can change shape by squeezing some segments to create extension others. As such, it can "provide structural support while allowing fine, dynamic control of the skin's three-dimensional texture," the researchers noted in their paper.
The octopuses had three dedicated types of muscles that control their on-call skin protrusions, or papillae. One set are shaped in concentric circles to lift the skin vertically away from the body. Another set pulls this form together, to determine the shape—whether it will be a round bump or tall spike. And a third group seems to pull the raised section back toward the surface, spreading out its base.
As the researchers wrote, this "retraction is important for quickly smoothing the skin for reduced drag during swimming, particularly for escape." Indeed, just watch the octopus go smooth as silk in the famous camouflage video as it jets away.
Learn more about the octopus's amazing camouflage abilities in Octopus! The Most Mysterious Creature In the Sea.
Illustration courtesy of Ivan Phillipsen