Cuttlefish have been mesmerising divers for decades. Their bodies pulsate with vibrant waves of colour, their tentacles splay out like delicate fingers and their fringe-like fins flutter vigorously in the current. These cephalopods - alongside squid and octopus - might be best known for their flashy colour-changing skills and otherworldly looks, but there is more to cuttlefish than meets the eye. From their marvellous memories to jet-propulsion abilities, discover our top ten cuttlefish facts about these fascinating creatures.
Cuttlefish Have Blue Blood
Living in the cold, oxygen-deficient ocean can be a tough gig. However, cuttlefish have a curious adaption to survive: greenish-blue blood. Red blood is caused by iron-rich haemoglobin. However, cuttlefish's blood doesn't hold haemoglobin but copper-rich hemocyanin, which is more efficient at transporting oxygen. Hemocyanin also turns bluish-green when it reacts with oxygen, hence the blue blood.
Cuttlefish Have More Than One Heart
Cuttlefish have a whopping three hearts. Two of these hearts are known as branchial hearts, while the third is called the systemic heart. The branchial heart pumps blood to the cuttlefish's gills where it gets oxygenated. Then, the systemic heart pumps the oxygenated blood around the cuttlefish's body. This helps support their remarkable agility and cognitive prowess.
Cuttlefish Can’t See Colour but Can Change Colour
Alongside octopuses, cuttlefish are often called the 'chameleons of the sea' due to their colour-changing abilities. What's even more impressive is that they can achieve an exact colour match despite being colour-blind. Cuttlefish have one cone cell in their retinas - humans have three - therefore perceive the world in black and white. However, colours have different wavelengths of light and cuttlefish are specially adapted to sense these wavelengths. Cuttlefish will use specialised skin cells called chromatophores to skilfully mimic their surroundings in the blink of an eye.
Male Cuttlefish Can Mimic Females
When it comes to mating, juvenile males are using their camouflage skills to gain a competitive edge over bigger males. These canny operators are mimicking females on one side of their body to trick larger rival males into thinking they're just seeing a group of females hanging out, giving them more time to woo the female.
There Are 120 Species of Cuttlefish
Out of the 120 species of cuttlefish, the flamboyant cuttlefish is the most famous of the bunch. Commonly found around Indonesia, the flamboyant cuttlefish earned its name for its ostentatious getaway tactics. When threatened, this crafty cuttlefish will move its fins and flash bright colours to show that it is poisonous. Worthy of another shoutout, the reaper cuttlefish - or red cuttlefish - is a bright red colour with two black spots on its upper body and can be found in the southwestern Pacific Ocean.
Cuttlefish Are Very Intelligent
Among octopuses, cuttlefish have an extremely large brain-to-body ratio, making them one of the most intelligent invertebrates. Cuttlefish have not only proved their ability to solve mazes and puzzles, but have also shown self-control. A 2020 study adapted the Stanford marshmallow test, giving cuttlefish the choice between something less tasty immediately - a piece of king prawn - or their favourite nosh - live grass shrimp - later. The result? The cuttlefish learned to wait for something better.
Cuttlefish Can Make a Quick Getaway
One of our least surprising cuttlefish facts is that cuttlefish use ink to help them make a quick getaway. When a cuttlefish feels threatened, it releases a cloud of ink - called sepia - into the water to distract predators. The cuttlefish will then expel a strong jet of water from its siphon to help it get away quickly. Usually, cuttlefish move much more gracefully by undulating the fringe running along the side of their body.
Cuttlefish Are Molluscs
Cuttlefish may not look like your typical mollusc, but they are molluscs, nonetheless. Instead of an external shell, they have a chalky internal shell called a cuttlebone, which is filled with gas to help control buoyancy.
Cuttlefish Have a Short Lifespan
Cuttlefish only mate at the end of their lives, which, at 20 months, is the human equivalent of 90 years of age. Unlike the rest of the animal kingdom, they also keep their memories until only a few days before their death. Scientists believe this is so they can remember who they have mated with to increase their chances of reproducing.
Cuttlefish Have Eight Arms and Two Tentacles
Cuttlefish have two tentacles - featuring suckers on their tips only - which they use for hunting. While they're swimming, their tentacles are usually tucked among their arms resting. However, when a cuttlefish is ready to strike its prey, it points its arms at its victim and its tentacles shoot out at lightning speed.
If these cuttlefish facts have you dreaming of diving, get in touch with our diving experts to learn the best places to dive with cuttlefish.