Type “cephalopod camouflage” into YouTube and be prepared to gasp. Cephalopods—which include octopuses, squid, and cuttlefish—can change their color, shape, and texture to blend in with their background.

“They are charismatic and very smart,” said Dan Distel, director of Northeastern’s Ocean Genome Legacy Center. “They’re the most intelligent invertebrates, as far as we know.”

As part of #CephalopodWeek, we asked Distel to dive into the world of cephalopods and explain why they are the smartest and stealthiest creatures in the sea.

How do we know that cephalopods are intelligent?

One example is that octopuses can solve complex problems. They can unscrew the lid of a jar to get food that’s inside.There is an octopus that uses coconut shells and hides inside of them. They’ve learned to move through mazes to find food. They’re incredible at fitting through very tiny spaces.

A couple of years ago, fish and even some sharks were disappearing from a public aquarium tank, and no one could figure out where the fish were going. Finally, workers discovered that an octopus had managed to sneak through the drain pipes and get into the tank where the fish were. The octopus was eating the fish and then going back to its own tank. It was very, very clever.

Squid also use color to communicate with one another. Two males display aggression to each other by making their skin white. If there is one squid on the left and one on the right, they will display white on the sides that are facing each other and display their normal coloration on the sides that are not facing each other. When they switch positions, they both switch their colors so that they’re still displaying white toward their rival. It’s really amazing.

What about their ability to camouflage?

Many cephalopods have this amazing ability to transform their color, their shape, and their appearance in general. Some cephalopods trick the senses of predators in order to hide from them—and they do it in a variety of amazing ways. They can actually make their skin mimic the color, texture, shape, and pattern of their background. They can make themselves look like a piece of seaweed on a rock or a piece of coral. They can make themselves look like predators, snakes, or fish. They also can use their coloration to shock or confuse other organisms by producing psychedelic patterns on their surfaces. They do some really remarkable things.

Why are cephalopods important for research?

Cephalopods help researchers study the nervous system. You may have heard of the squid giant axon. Squid have some very, very large nerve cells. Most mammals’ nerve cells are very slender and it’s very difficult to, say, put a probe inside of a nerve cell. But squid have giant nerve cells, so early on in the study of neurobiology, people started using squid nerve cells because they’re so big and easy to take measurements. You can put probes all along their length. A lot of the basic chemistry of how a nerve signal is transmitted along the nerve cell was worked out in the giant squid axons.

Other research looks at how squid camouflage themselves and what it can teach us about our own perception. In other words, it’s not just a matter of looking like your background. You’ve got to look like what your predator thinks the background looks like, taking their perception into account.

Researchers at Northeastern are using squid skin pigment to make thin films and fibers that could be incorporated into textiles, flexible displays, and future color-changing devices.

Have you ever encountered a cephalopod during any of your dives?

Oh sure. They’re always fun to see. I can recall seeing a really cute family of squid in Bonaire, an island in the Caribbean Sea, and they would line up from largest to smallest and swim together in parallel. It’s just really funny how they do that. We see octopuses from time to time and they’re just remarkable creatures.

Cephalopods are just one of the families in the mollusk phylum. Mollusks are the most diverse invertebrate phylum and they include everything from worms and snails to clams and squid to octopuses and cuttlefish. It’s an amazing diversity of life in that group. And squids go from among the smallest animals in the ocean to among the largest.