The Insane Biology of: The Cuttlefish.

We tend to think of octopuses as the top cephalopod of the ocean, smart, curious, mischievous, and colorful. But all those same adjectives can be applied to cuttlefish, and then some. Cuttlefish are as smart as an octopus, and arguably more extravagant when it comes to their color displays, a surprising ability considering they are thought to be colorblind. They share a lineage with octopuses, their last common ancestor comes from about a hundred Cuttlefish have eight short arms and two long tentacles, and their eyes have a strange W-shaped pupil. And they aren't quite as jello-y as an octopus. Cuttlefish have their very own hard internal structure called a cuttlebone. Cuttlefish also evolved an incredible brain thanks to spending millions of years as prey for pretty much everything. Some species even have a larger brain-to-body ratio than octopuses. Scientists have even trained them to go through mazes. Other researchers have found that cuttlefish have a good enough memory to understand the relationship between how much prey they eat and how often the food source will be replenished. In other words, episodic-like memory that was previously only attributed to mammals and a few birds. Cuttlefish are a small but mighty ocean creature. How are cuttlefish able to match the pattern and color of their skin to their environment when they can't even see color? And beyond hypnosis, what is all that flashing for? Just how smart are cuttlefish, and are they perhaps the superior cephalopod of the sea? Despite their name and despite being cute, cuttlefish are not known for cuddling. Cuttlefish are cephalopods that live in tropical and temperate waters worldwide except the Americas, and they generally live in the shallows near reefs or seagrass beds. There are around 120 species of cuttlefish, which generally range in size from 15 to 25 centimeters. The smaller species, like the flamboyant cuttlefish, are as small as 8 centimeters. And the largest species, the giant Australian cuttlefish, can reach up to 1 meter and weigh over 10.5 kilograms. But where exactly did their name come from? The name comes from the Old English word for them, coudel, but scholars aren't really sure where it came from or what it might mean. We've also called them inkfish, sea cat, sea sleeve, or sepioid at different times. Turns out humanity has a long history of being entranced by these creatures. Going back to Greek and Roman antiquity, cuttlefish were prized for their ink, which produced a long-lasting brown pigment used for writing and coloring cloth. In fact, that's what gave them their name in those languages, sepia. Like the color sepia, which is also the genus name for many species of cuttlefish. Maybe it's impossible for humans to land on a perfect name for them because cuttlefish are just so weird. For swimming sea creatures, a major component of getting around the ocean is having some kind of buoyancy system. For fish, that's the swim bladder. For larger animals like whales, a large store of fat provides buoyancy. But cuttlefish have an utterly unique buoyancy mechanism, the cuttlebone. Although its name suggests it's something similar to any of our bones, the cuttlebone is nothing like the bones we have. A cuttlebone has high porosity and high permeability, meaning it has lots of small voids throughout its structure. But it also has high stiffness, meaning it can resist changes in shape when being acted on by a physical force. These physical properties are generally in opposition to each other. Usually materials become stiffer by adding more material and becoming less permeable and vice versa. But the cuttlebone has two main structures that cause these properties to coexist. The dorsal shield is a thick, tough layer that acts as the base for the lamellar matrix. And the matrix is the region that looks like corrugated cardboard with many layered chambers. This is all very complex and very strange. Why did such a weird structure evolve? Because all of these materials act together to help the cuttlefish regulate its buoyancy while also withstanding external pressure that increases with water depth. With this porous material, the cuttlefish can control how much liquid enters the cuttlebone, so that the ratio of gas to liquid changes based on their depth and how buoyant they need to be. The more gas in the bone, the more they will float. The more liquid, the more they will sink. Having this buoyancy device inside them means it's much easier for the cuttlefish to be neutrally buoyant than it is for either the octopus or the squid who don't have a bone like this. In fact, cuttlefish spend more than 95% of their time just chilling, hovering with neutral buoyancy. But even though the cuttlebone can withstand some external water pressure, it can't do so forever. Therefore, cuttlefish can't go very deep, since higher pressures over a couple hundred meters would crush their cuttlebone and kill them. Researchers have shown that the cuttlebone is pliant enough that it wouldn't fail catastrophically if it went a little too deep, but they still aren't adapted for high pressures. So even though there are deep-sea squid and octopuses, there are no deep-sea cuttlefish. They're stuck living in coastal areas closer to the surface. In the case of the tiny flamboyant cuttlefish and its cousin, the paint pot cuttlefish, the cuttlebone is slightly less useful as a buoyancy device. These species live in sandy patches of the Indo-Pacific and barely reach 3 inches or 8 centimeters in size, meaning that their cuttlebone is tiny. And that little cuttlebone causes them to not hover very well. Instead, these two species use a strange type of locomotion known as ambling. They use several arms and fins to make leg-like stumps, which they use to slowly creep across the seafloor, camouflaged to look like sand so that they can sneak up on tiny shrimp, crabs and fish. This camouflage helps them avoid detection while hunting. But if the flamboyant cuttlefish is spotted by a predator, it turns off its camouflage, so to speak, and uses the opposite approach to scare off its hunter. Vivid, flashy, flamboyant colors. Color-capable fish predators are suddenly startled by the instantaneous change in appearance of the cuttlefish, and this disrupts their attack sequence. Outlined in fluorescent yellow, both species also use pulsing bands of black, a pattern known as passing clouds. Such vibrant coloration has led scientists to wonder if the flamboyant cuttlefish might Experiments have revealed trace amounts of the neurotoxin tetrodotoxin, or TTX, in their flesh. But the rates of toxin in the cuttlefish are so low that it would be unlikely to kill a predator. It's an ongoing area of investigation, but even without the possibility of poison, the flamboyant cuttlefish seems to be doing pretty well with their alarmingly vibrant display. And they're not the only species to use color to their advantage. A distinguishing feature of cuttlefish is their ability to instantly camouflage themselves in any environment they settle in. This is truly remarkable because coral reefs are the most diverse and complex visual environments on the planet, land, or sea. And cuttlefish can look exactly like coral, seagrass, sand, or rock. Part of cuttlefish camouflage comes in 3D. Cuttlefish have a unique feature in their skin called dermal papillae. They're made up of erector muscles in the skin, which lifts bumps in the skin into a variety of different shapes that can match the surrounding 3D texture of algae, coral, or rocks. And with this changing texture comes mesmerizing changing colors and patterns. First in the skin are the chromatophores, organs that cuttlefish have by the millions. These organs have an elastic sack of colored pigment granules, which can be expanded by tiny muscles controlled by neurons in the brain. As the muscles flex, the pigment sack expands horizontally and reveals itself over a larger area, sort of like stretching a water balloon full of food coloring. But chromatophores are generally only yellow, red, or brown, and cuttlefish clearly use more than those three colors or color combinations. Their shiny iridescence comes from the iridophores, which are thin cells stacked on top of each other that reflect light at different wavelengths, making them appear any color of the rainbow depending on the spacing of the reflecting platelets and on the angle from which they're observed. And lastly are the leucophores, a different type of reflective cell that makes their skin look white, which is one of the most complex colors. Collectively, these three types of skin coloration enable cuttlefish to put on dazzling displays. And with direct control from the brain, this change in skin color occurs in less than 200 milliseconds, faster than the blink of an eye. And it's even more impressive when you learn that cuttlefish can't even see color. Their eyes contain just one kind of color-sensitive protein, which restricts them to a monochrome view of the world. So if they can't even see the colors, how on earth do they match them? One possibility is that cuttlefish see with their skin, enabled by light-sensitive proteins called opsins that have been detected in their skin. But a more recent theory proposes that while cuttlefish don't see colors like we do, they might perceive them in a different way, through chromatic aberration. This is the phenomenon where different colors of light come into focus at different distances because of the way different wavelengths of light bend through a lens. Short wavelengths, blue light, get refracted or bent more than long wavelengths, red light. We've all seen this happen with a glass prism. For us, chromatic aberration is a nuisance. It sometimes shows up in photos annoyingly, or is why when you get your eyes dilated at the eye doctor, everything gets a fuzzy, rainbow outline. But perhaps cuttlefish use this phenomenon to their advantage. Those weird, W-shaped pupils let light in from many different angles, enhancing the chromatic aberration phenomenon. They could hypothetically separate reds, yellows, and blues based on their wavelength, allowing them to detect color by detecting differences in blurring as focus changes. So rather than seeing different colors as we know them, they are detecting different levels of blur. And cuttlefish have another peculiar capability. They can see in the dark and dynamically change their camouflage to different backgrounds, as if it was high noon with all the colors available. In a field study in Australia, followed by lab experiments at the Marine Biological Laboratory in Woods Hole, scientists verified cuttlefish abilities to instantly change camouflage on different backgrounds, even when light was at its dimmest, with only faint starlight available. For humans and many animals, this little light would mean they can't see anything. So for a cuttlefish to not only see, but see well enough to still match their background is impressive by any comparison. But the cuttlefish's color-changing abilities aren't only useful for hiding. Some cuttlefish seem to use them for hunting. For most cuttlefish, hunting can normally be divided into four distinct phases. Detection, positioning, strike start, and prey seizure. The detection phase occurs when the cuttlefish first notices its prey. The eyes then focus on the prey, and the cuttlefish slowly turns its body so that the arms and head are oriented towards the prey. And at this point, during the positioning phase, is where some cuttlefish, like the broad club cuttlefish, get creative. It will begin a rippling, strobe-like effect that seems to mesmerize their prey, making it easier for the cuttlefish to get close enough without the prey fleeing. At this point, the tentacles begin pointing towards the prey, but they hold their fire. Then, once the predator-prey distance is approximately one mantle length, the tentacles abruptly shoot out with extreme speed. Getting their aim right before they shoot is of the utmost importance, because once the tentacles are released, the cuttlefish loses all motor control of them and has no further ability to readjust the aim or speed. But with any luck, the cuttlefish will snatch their prey up, striking like lightning, before the unsuspecting animal even knows what's going on. Hypnotic hunters and master camouflagers, the cuttlefish use their color patterning to survive in the cutthroat competition of the ocean. But the usefulness of rapid adaptive coloration doesn't stop there. It's also crucial in another aspect of their life, mating. Unlike most other animals with large brains, most cephalopods aren't particularly social. Most of the time, they hunt and live alone. The main exception to this solitary lifestyle is during mating. And as researchers have learned more about the courtship behavior of cuttlefish, they've discovered something interesting in several species. It's not always the biggest males who win. Giant cuttlefish that live around Australia will congregate for mass breeding, with females sometimes being surrounded by as many as 11 males. The larger males will put on elaborate displays to intimidate other males, and will also guard the females so they can't be accessed by any other potential suitors. But some of the smaller males use their changeable appearance to their advantage in these situations too, for deception. Smaller males will actually mimic the appearance and posture of females, slip past their larger male adversaries who think they're gaining another mate, and the sneakers then mate with the females while the large males actually guard them. And surprisingly, DNA analysis of the fertilized eggs found that the small, sneaker males who impersonated female cuttlefish were successful in about 60% of their attempts. About twice the success rate of the larger, honest males. A similar strategy is used by a different species, the mourning cuttlefish. But they take the disguise to a whole nother level. When a male mourning cuttlefish finds itself in a situation where only one rival male is present, along with one female, the male will split its color displays in half, straight down the middle. For the side facing the female, the male will present its normal male colors. For the side facing the rival male, it will display female colors to avoid being perceived as a threat. It pays off to be a little deceptive when it comes to being a cuttlefish. You're more likely to catch your favorite prey for dinner, to avoid being someone else's dinner, and to pass on your genes to the next generation. And it takes a certain level of intelligence to pull off a trick like this, which is something cuttlefish have in spades. One of the most intriguing aspects of a cuttlefish is the way their minds work. Scientists long believed that only vertebrates like great apes, elephants, and corvids could demonstrate any form of complex intelligence. And they had two hypotheses to explain how intelligence evolved in these organisms. The ecological intelligence hypothesis suggests that the physical demands of locating food and determining when it's best to eat it, like the ripeness of fruit or the level of decomposition in meat, triggered the development of intelligence in our hominin ancestors. The social intelligence hypothesis, on the other hand, suggests cognition is the result of living in a social group, whether that means dealing with competition or collaboration. Cuttlefish, squid, and octopuses are all invertebrates without an interior skeleton or spine, and they diverged from vertebrates more than 550 million years ago. So their particular intelligence can't be directly related to that of vertebrates. And these species are mostly not very social, which contradicts the social intelligence hypothesis. In the case of these cephalopods, researchers believe it's a combination of needing to forage in a complicated environment, needing to avoid being eaten by predators, and needing to fiercely compete for reproductive success that pushed the animals to develop uncanny intelligence. And the cuttlefish have an impressive number of abilities that mark their intelligence. The pharaoh cuttlefish have number sense, the ability to distinguish between groups based on the quantity within them. They have both short and long-term memory and can adjust their hunting strategies based on past experiences and future expectations. Researchers have consistently found that cephalopods have a larger brain-to-body ratio than fish and some reptiles, and that their big brains are related to their visual systems, short and long-term memory, and their system for camouflage and communication. Some cuttlefish also have a larger brain-to-body ratio than octopuses. So does that mean cuttlefish are smarter than their octopus cousins? It's hard to say. Both organisms have big brains, good memories, the ability to learn, and excellent camouflage skills. They also show different types of abilities, like the octopus that carries shells with it so it has a home, or the way male cuttlefish will disguise themselves as females for mating purposes. Determining which one is smarter is ultimately impossible, because they have different bodies, different habitats, and different behaviors. What we can say for sure is that all the cephalopods are a lot smarter than we once gave them credit for. Despite fierce ecological competition, climate variations, fishing pressure, and pollution, the cuttlefish lineage has managed to survive more than 100 million years, and is still doing well in many parts of the world. So maybe if there's a lesson to be learned from them, it's this. Don't be afraid to be a little weird, or maybe a little sneaky. There's something truly beautiful about pondering the complexity of evolution throughout the billions of years life has existed on this planet. How a single cell becomes many, reproducing, mutating, giving rise to the sponges, worms, and jellyfish. The invertebrates and the vertebrates, the cephalopods, birds, reptiles, mammals, and eventually us. There have been so many pivotal moments during the course of evolution that resulted in the world we know today. And these moments are so fun to explore with the free-to-play game called Cell to Singularity. Cell to Singularity is a non-fiction game available on Steam, iOS, and Android that takes you through evolution, where you start as a single-celled organism and progress through the tree of life. Each biological upgrade brings you closer to engulfing an entire planet with a civilization on the brink of technological singularity. The game also has limited-time events that run weekly. 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