A Mollusk With a Mind

by Belinda Recio

Octopus researchers often say that if we want to imagine what extraterrestrial intelligence might look like, we need look no further than the octopus. With eight limbs that attach to the head and three hearts that pump blue blood, octopus anatomy is undeniably otherworldly.

His boneless body can squeeze through any opening larger than his beak, located where his arms meet. Inside his mouth is a toothed tongue and flesh-dissolving neurotoxin saliva. Each octopus arm has roughly two hundred suckers, which can fold together for grasping. Each sucker has about 10,000 receptor cells for touch, taste and smell, which makes octopuses about a thousand times more sensitive to those stimuli than humans.

The octopus can vanish in a cloud of ink that he blasts out of his siphon—a tube-like structure that he also uses to swim (shooting water out of it in a kind of jet-propulsion technique), move objects, uncover prey buried in sand, clean his den and blast away unwanted annoyances. The octopus is also a tool user. He stacks stones and other objects at the entrance to his den, presumably to create smaller openings less easily penetrated by predators. Some use stones as wedges to prop open the shells of bivalves so they can access the edible flesh. Others collect discarded coconut shells and assemble them into clamshell-like mobile homes.

One of the most dramatic examples of octopus tool use is by a group known as the blanket octopuses, named after the arm webs of adult females. Blankets are immune to the venom of the Portuguese man o' war jellyfish, so when they run into one, they sometimes help themselves to a venomous tentacle by breaking it off. Then, with their webs trailing behind them like cloaks, they use the toxic tentacles as “swords” to ward off predators.

As fascinating as all of this is, what makes an octopus really stand out is his neurological system, which is very different from ours. The octopus's brain—the largest of any invertebrate—contains roughly 400 million neurons. This number, in itself, is not so impressive. It's more neurons than a guinea pig has (240 million), but much less than a cat (760 million), and significantly less than a human (86 billion). What is impressive is that roughly half of an octopus's neurons are located in his eight arms. This is why, when an octopus loses an arm, for hours afterward the severed arm can still crawl around and pick up objects.

But these arms with minds of their own don't just have motor control skills—they can "see," too. Scientists discovered that the skin of certain octopus species contains the same light-sensitive proteins found in their eyes. This enables their arms to detect light and discern brightness levels, which are then used to determine his appearance. The octopus changes the color, pattern and texture of his skin to communicate mood and readiness to mate, blend into his surroundings or mimic another species.

Once an octopus decides how he's going to appear, his three layers of skin and muscles take over. Each skin layer contains pigment sacs surrounded by a ring of muscles. When the octopus flexes his muscles to expand the sac, the pigment is revealed. His outer layer of skin creates colors such as yellow, orange, red and black; the middle layer creates blues and greens; and the deepest layer produces white light, which acts as a canvas for the other colors. The muscles receive signals from the octopus's brain and arms and can change colors and patterns in less than a tenth of a second.

The octopus can change his texture, too. Using another set of muscles, he can raise his skin into peaks or flatten it into smoothness, making himself look like a rock, coral, seaweed or other species. One species—the mimic octopus—avoids predators by impersonating lionfish, sea snakes and certain species of flatfish, all of which are highly poisonous. Amazingly, the mimic seems to know which deadly creature he should impersonate based on who-eats-who ecology. For example, when a mimic is attacked by damselfishes, he often imitates a banded sea snake, a known predator of damselfishes.

So how do we make sense of octopus intelligence? Dr. James Wood, a cephalopod research- er, once suggested we think about the intelligence of other species this way: "Imagine if an octopus made an intelligence test for humans. It might have a question that goes, 'How many color patterns can your severed arm produce in one second?'" Wood's question reminds us that when it comes to the intelligence of other animals, we need to consider how our human bias impacts the way we study the intelligence of other species

Adapted in part from Inside Animal Hearts and Minds by Belinda Recio, published by Skyhorse Publishing, 2017

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