Internal shell (cuttlebone)
A unique internal cuttlebone used to control buoyancy.
Photo byPeter Boshra
Species Guide
What to know about cuttlefish
A clean field guide focused on habitat, identification, behavior, and conservation context without burying the useful parts.
Cuttlefish are marine cephalopod molluscs in the family Sepiidae. They possess a unique internal shell called the cuttlebone that aids buoyancy, large W-shaped pupils, eight arms, and two tentacles with denticulated suckers used to seize prey. Typical sizes range from about 15–25 cm (6–10 in), while the largest species (Sepia apama) can reach about 50 cm mantle length and over 10.5 kg. Diets include small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish. Typical life expectancy is around 1–2 years. Cuttlefish are noted for high relative brain size and are considered among the most intelligent invertebrates. They also release a brown pigment (sepia) when alarmed.
Commonly cited pressures include Predation.
Feeds on small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish.
Identification
How to identify cuttlefish
The visual markers divers can use underwater, plus the species most likely to cause confusion.
Key identification markers
Eyes and pupils
Large eyes with distinctive W-shaped pupils.
Arms and tentacles
Eight arms and two tentacles furnished with denticulated suckers for capturing prey.
Size range
Most species about 15–25 cm; giant cuttlefish (Sepia apama) up to about 50 cm mantle length and over 10.5 kg.
Common lookalikes
Other cephalopods
Squid and octopuses are related cephalopods with similar overall body plans.
Diet
What cuttlefish tend to eat
Useful feeding context that often explains habitat, movement, and encounter style.
Feeds on small molluscs, crabs, shrimp, fish, octopuses, worms, and other cuttlefish.
Conservation
What is happening with Cuttlefish
Status, pressure, and protection context grounded in cited sources rather than filler.
Commonly cited pressures include Predation.
Main threats
Predation
Natural predators include dolphins, larger fish (including sharks), seals, seabirds, and other cuttlefish.
Responsible Encounters
How to dive with cuttlefish
Conservation-minded guidance for divers who want the encounter without adding pressure.
Give cuttlefish space, avoid blocking the animal's path, and follow local site and operator rules for wildlife interactions with molluscs.
Field Notes
Interesting things worth knowing
Useful species context that makes the encounter more meaningful once you are underwater.
Field notes
Ink and sepia
They release a brown pigment (sepia) when alarmed; this pigment gave its name to the color sepia.
Short lifespan
Typical life expectancy is about 1–2 years.
Relative brain size
Cuttlefish have one of the largest brain-to-body size ratios among invertebrates.
FAQ
Frequently asked questions
Clear planning and conservation answers written for search visibility and AI retrieval.
Research Sources
Cuttlefish information sources
Primary and credible references behind the field-guide and conservation claims on this page.
Sources 4Last Updated
WoRMS - World Register of Marine Species - Sepiida · Reference · WoRMS
Primary wildlife guide source.
OBIS · Reference · OBIS
Supporting wildlife source.
Britannica · Reference · Britannica
Supporting wildlife source.
Cuttlefish · Encyclopedia · Wikipedia
Supporting wildlife source.
Related Species
More in Molluscs
Related species guides in the same encounter family.