What are Cuttlefish?

Mary McMahon
Mary McMahon

Cuttlefish are marine mollusks in the order Sepiida, with around 100 species known to exist on Earth. These mollusks are closely related to their fellow Cephalopods like octopi and squid, but they have a few unusual traits which set them aside from their relatives and other marine animals. Humans are interested in cuttlefish for a number of reasons, ranging from a potential food source to a rich field of research, although many laypeople are not familiar with these unusual and actually rather fascinating mollusks.

Cuttlefish are marine mollusks that are related to octopi and squids.
Cuttlefish are marine mollusks that are related to octopi and squids.

Although the common name includes the word “fish,” cuttlefish are not fish at all. They more closely resemble their relatives the squid, with 10 grasping arms and a unique calcium-rich inner shell known as the cuttlebone. The cuttlebone can be filled with varying levels of gas to adjust the buoyancy of the cuttlefish, and these animals move with the use of jet propulsion, using their complex fins to control their path through the water. Although cuttlefish are not quite as rapid as squid, they are very fast movers.

Speed isn't the only weapon of the cuttlefish. These creatures are capable of ejecting ink in self defense, like their relatives, and they can also change the color and texture of their skins for camouflage. In addition to changing color to blend in, cuttlefish also change their color to send signals to other cuttlefish, and some species are quite flamboyant, generating intense displays of red and orange.

Cuttlefish have three hearts to pump their copper-rich blue to green blood. Each gill has a dedicated heart, with the third heart handling general circulation in the body. These animals require three hearts because their blood is not very efficient at oxygen transport, so they need to work harder to get oxygen through their bodies. The eyes of a cuttlefish are also unusual, with very distinctive W-shaped pupils, rather than the classic rounded or vertical pupil most people would expect to see.

Cuttlefish ink, known as sepia, has been used for centuries by humans for writing, and cuttlefish are used as a food source in some regions of the world. The cuttlebone is also useful as a dietary supplement for pet birds, many of whom need additional calcium in order to thrive. Biologists are very intrigued by the cuttlefish, because these mollusks are extremely intelligent and very social. By studying cuttlefish intelligence and behavior, researchers hope to learn more about the different kinds of intelligence on Earth, and how they interact.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

You might also Like

Readers Also Love

Discussion Comments


This post reminded me of this cuttlefish changing color very fast. I wonder if octopuses can change their colours as fast as them. --Angela


I've had Cuttlefish in Spain as my first meal of being there. I doubt it was jetlag but it tasted horrible. Squid is actually nice and used regularly in paellas - obvious why this isn't!


@stl156 - I know what you mean. A lot of the Asian food combinations sound pretty odd at first. I'm a pretty brave food eater, though, so I would definitely try it if I got the chance. Usually the dishes aren't as bad as what you would expect. That being said, I've definitely had my fair share of disgusting food.

Has anyone ever tried the "meat" of cuttlefish? I'm sure it would probably be like squid.

Besides research on intelligence, do cuttlefish have any other sort of scientific use? I read that they can create toxins like octopuses do. Can any of those be used for special medicines, or are all of the uses still unknown?


After I read this, I went and looked at some cuttlefish pictures. I don't know why, but for some reason, I was always under the impression that cuttlefish were a bright colored fish kind of like the clown fish. I guess I got fooled by the name.

I was reading about the ink, too. I have heard of the color sepia, but never knew that the name came from the ink from octopuses and such. They even use the ink of cuttlefish in some Asian dishes.

One popular dish is to mix the ink with rice noodles. I'm curious to know what the taste is like, but I don't think I would bring myself to try it. I'm sure it doesn't taste anything like ink from a pen, but that's all I would be able to think of. Has anyone here ever had anything that used ink from a cuttlefish or squid or something?


@TreeMan - I'm actually writing about cuttlefish adaptations for a biology class I am in. Oddly enough, cuttlefish are found in shallow waters of every continent except for North and South America. I haven't found a good explanation why. The normal cuttlefish lifespan is a little over one year usually.

From the research I've been doing, I'd have to say the ability for cuttlefish to change the color of their skin is the neatest adaptation. They have a lot of big predators like dolphins and sharks, so it pays to be able to hide well. The ink is interesting, too, just because it is such a unique defense to Cephalopods.


Wow, I have heard of cuttlefish, but I didn't realize how cool they are. I'm wondering, though, why is their blood rich in copper? I didn't know there was a lot of copper in seawater to begin with.

Also, what do cuttlefish eat? I want to say I've seen TV shows where octopuses are eating starfish and maybe other mollusks like clams. Do cuttlefish eat the same types of things? Where in the oceans are cuttlefish found? As in, what specific oceans and what depth? I am really interested in these now.

Post your comments
Forgot password?