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Science & Nature • Marine Biology

Cuttlefish

Cuttlefish are marine cephalopod molluscs in the order Sepiida, related to squid and octopuses.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Cuttlefish are marine cephalopod molluscs in the order Sepiida, related to squid and octopuses. They are known for their internal cuttlebone, ability to change colour, and short life cycles. More than 120 living species are recognised, and they occur mainly in tropical and temperate seas.

Classification and evolution

Cuttlefish belong to the cephalopod class within the molluscs and are placed in the order Sepiida. They are part of an ancient lineage of ocean-dwelling animals related to squid, octopuses, and nautiluses.

Physical characteristics

Cuttlefish have a soft body, large eyes, eight arms, and two tentacles. Their internal cuttlebone is a gas-filled shell used for buoyancy control, and many species can rapidly change colour and pattern.

Habitat and distribution

They live in tropical and temperate marine waters around much of the world, usually in shallow reefs, seabeds, seagrass meadows, and coastal channels. Sources note relatively few species in the Americas.

Behaviour and diet

Cuttlefish are predatory and use their vision, colour change, and camouflage to hunt. Their diet commonly includes shrimp, crabs, and other molluscs.

Conservation status

Most cuttlefish species are not currently considered threatened, although data are incomplete for many species. The giant Australian cuttlefish is listed as Near Threatened.

Key facts

  • Cuttlefish are not fish; they are cephalopod molluscs.
  • They have an internal shell called a cuttlebone that helps control buoyancy.
  • They are widespread in marine waters, especially in shallow coastal habitats.
  • Cuttlefish are active predators that feed on crustaceans and other molluscs.
  • They typically live only one to two years and often die after breeding.
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Canadian context

Cuttlefish are not native to Canadian freshwater systems, but Canadian readers may encounter them in marine biology, aquarium contexts, seafood discussions, or studies of cephalopod behaviour and conservation.

Frequently asked questions

Are cuttlefish fish?
No. Cuttlefish are molluscs in the class Cephalopoda, not fish.
What is a cuttlebone?
A cuttlebone is the internal shell of a cuttlefish, used to help control buoyancy.
How many species of cuttlefish are there?
There are more than 120 recognised species of living cuttlefish.
What do cuttlefish eat?
They mainly eat crustaceans such as shrimp and crab, and also molluscs.
How long do cuttlefish live?
Most species live about one to two years, with many dying after the breeding season.
Where do cuttlefish live?
They are found in marine waters worldwide, especially shallow coastal habitats, reefs, and seagrass areas.

References

  1. PBS Nature — https://www.pbs.org/wnet/nature/blog/cuttlefish-fact-sheet/
    Supports: Taxonomy, number of species, and conservation notes including the giant Australian cuttlefish's Near Threatened status.
  2. PBS Nature — https://www.pbs.org/wnet/nature/animal-guide-cuttlefish/1161/
    Supports: General biology, habitat, distribution, diet, lifespan, size, and species count.
  3. Science Focus — https://www.sciencefocus.com/nature/everything-you-wanted-to-know-about-cuttlefish
    Supports: Cephalopod classification, cuttlebone, habitat, diet, lifespan, and distribution.
  4. The Wildlife Trusts — https://www.wildlifetrusts.org/wildlife-explorer/marine/squids-octopuses-and-cuttlefish/common-cuttlefish
    Supports: Common cuttlefish biology, cuttlebone, behaviour, habitat, lifespan, and UK distribution.