1. Cuttlefish have not one, not two, but three hearts! Two hearts are used to pump blood to the cuttlefish's large gills, and the third heart is used to circulate oxygenated blood to the rest of the body. Speaking of cuttlefish blood, even that's interesting. According to New World Encyclopedia, "The blood of a cuttlefish is an unusual shade of green-blue because it uses the copper-containing protein hemocyanin to carry oxygen instead of the red iron-containing protein hemoglobin that is found in mammals."
2. In an effort to hide from predators, cuttlefish can mimic the shape and texture of objects around them. Their close relative, the octopus, is also able to do this. Cuttlefish accomplish this texture change by extending or retracting tiny bumps called papillae located across their bodies, and thus better match sand, bumpy rocks or other surfaces where they're hiding.
3. Cuttlefish males disguise themselves as females to get past competing males to mate with a female. According to Mental Floss, to woo a female without attracting competing males, "wily male cuttlefish employ some tricky gender-bending camouflage. With one half of their body they put on a colorful display for the female's benefit. With the other half, they disguise themselves as another female, mimicking the muted tones of the female they're courting so as not to attract the attention of nearby males." But that's not all they'll do. If a male isn't as big and tough as other males vying to mate with a female, then he'll rely on cunning and stealth instead. A male will mute his colors, position his body to look like a female carrying eggs, and use this disguise to sneak past competing males for his opportunity with the female.
4. Cuttlefish eat less for lunch when they are expecting a big dinner. When they know that shrimp -- their favorite food -- will be available later in the day, cuttlefish will eat fewer crabs earlier on. Researchers say this ability to make decisions based on future expectations shows that cuttlefish have complex cognitive abilities. "It was surprising to see how quickly the cuttlefish adapted their eating behavior - in only a few days they learned whether there was likely to be shrimp in the evening or not. This is a very complex behavior and is only possible because they have a sophisticated brain," Pauline Billard, a PhD student in the University of Cambridge's Department of Psychology, and lead author of the study published in Biology Letters.
5. Cuttlefish have truly impressive vision, including the ability to see what's behind them — completely. According to PBS, "It can see well in low light and can also detect polarized light, enhancing its perception of contrast. While we humans reshape our lenses in order to focus on specific objects, the cuttlefish moves its lenses by reshaping its entire eye. Also, the cuttlefish's eyes are very large in proportion to its body and may increase image magnification upon the retina, while the distinct 'W'-shaped pupil helps control the intensity of light entering the eye.”
6. Cuttlefish count better than most human babies. A study published in the Proceedings of the Royal Society B found that 1-month-old cuttlefish could easily tell the difference between a box with four shrimp and a box with five shrimp. By contrast, 1-year-old human babies can only determine a difference between piles of one and two and piles of two and three, but no higher than that. When the boxes contained more shrimp, the cuttlefish took longer to decide which box to eat from, and researchers took this as a sign that the cuttlefish were physically counting the number of shrimp before making their decisions.
7. Cuttlefish are perhaps best known for their ability to almost instantly change color to match their surroundings, even as they swim through different colors of coral or rocks. What's more, is the coloration doesn't have to be static. They can change color in rapid patterns that make it look like ripples of color are rolling over their bodies. The mesmerizing "light show" effect is a strategy that can help cuttlefish catch prey. This detailed color-changing ability is even more impressive when you consider that cuttlefish are colorblind!
Watch the changes in action and learn more details about the incredible camouflage ability of these invertebrates in this video:
Editor's note: This story has been updated with new information since it was published in May 2016.