cephalopod

Introduction
General features and importance to humans
Natural history
- Reproduction and life cycles
- Behaviour
- Locomotion
- Ecology
Form and function
Evolution and paleontology
Classification
- Distinguishing taxonomic features
- Annotated classification
- Critical appraisal

References & Edit History Quick Facts & Related Topics

Images & Videos

A blue-ringed octopus with bright blue rings on its beige body crawls over a rocky, coral-strewn seabed.

Follow researchers into the waters off Vancouver Island in search of the giant Pacific octopus

A blue-ringed octopus, Hapalochlaena maculosa, with bright blue rings on its yellow body and arms, is shown against a black background.

Observe a cuttlefish changing its colour as it swims near the Great Barrier Reef, off the coast of Australia

Image shows a reconstruction of squidlike creatures swimming.

A nautilus mollusk with a spiral, brown-and-white striped shell and numerous white tentacles extending from its soft body, set against a dark background.

At a Glance

cephalopod summary

Quizzes

Sea otter (Enhydra lutris), also called great sea otter, rare, completely marine otter of the northern Pacific, usually found in kelp beds. Floats on back. Looks like sea otter laughing. saltwater otters

Animal Group Names

Deadliest Animals Quiz

Match the Baby Animal to Its Mama Quiz

The bearded vulture (Gypaetus barbatus) is seen in Switzerland on December 2024

Animal Factoids

Related Questions

How are octopuses different from squids and cuttlefishes?
How are squid tentacles different from squid arms?
How deep can squids and octopuses live?
How did the cephalopod shell change during evolution?
How did veined octopuses use coconut shells as portable shelters?
How do bottle-tailed squids use glowing bacteria to produce light?
How do cephalopod beaks and radulas process food?
How do cephalopod suckers help capture prey?
How do cephalopods breathe with gills inside the mantle cavity?
How do cephalopods change their skin texture to resemble sand, coral, or seaweed?
How do cephalopods use colour patterns for camouflage and defense?
How do cephalopods use the mantle and funnel for jet propulsion?
How do chromatophores allow octopuses and cuttlefishes to change colour?
How do cuttlefish and squid breeding migrations affect where they are found?
How do octopuses affect lobster fisheries?
How do octopuses care for their eggs?
How do octopuses crawl across the ocean floor?
How do photophores produce light in squids and cuttlefishes?
How do squid fins help with swimming and hovering?
How does a squid steer while using jet propulsion?
How does hemocyanin make cephalopod blood blue?
How does the cephalopod brain support learning and memory?
How large can the giant Pacific octopus become?
How long do smaller octopuses and inshore squids usually live?
How many arms and tentacles do octopuses, squids, and cuttlefishes have?
How many living cephalopod species are there?
How quickly can cephalopods change colour?
What do octopuses, squids, and cuttlefishes eat?
What evidence shows that octopuses can learn?
What role does the hectocotylus play in cephalopod mating?
When did ammonites become extinct?
Where do cephalopods live from shallow coastal waters to the deep sea?
Which animals prey on cephalopods in the ocean?
Which cephalopod species can live in low-salinity bays along the Florida coast?
Which cephalopods do not have an ink sac?
Why are cephalopods absent from the Baltic Sea?
Why do active cephalopods need a closed circulatory system?
Why do cephalopods have three hearts?
Why do many cephalopod young develop without a larval metamorphosis?
Why does Nautilus have about 90 suckerless appendages?
Why does squid ink sometimes form a decoy shaped like the squid?
Why is veined octopus behavior considered a documented example of invertebrate tool use?
Why were squid giant axons important to studies of nerve impulses?
How does the giant squid compare in size to the colossal squid?
What is the conservation status of the giant squid?
When was the first video footage of an adult giant squid captured?
How does the colossal squid compare in size to the giant squid?
Where can different species of blue-ringed octopuses be found?
Are the blue-ringed octopuses poisonous?
What is the largest squid?

Science Insects & Other Invertebrates Mollusks

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External Websites

Paleontological Research Institution - Digital Atlas of Ancient Life - Class Cephalopoda
National Center for Biotechnology Information - PubMed Central - Evolution of cephalopod nervous systems
Monterey Bay Aquarium - Cephalopod
University of California Museum of Paleontology - The Cephalopoda
Animal Diversity Web - Cephalopoda
Food and Agriculture Organization of the United Nations - Cephalopods (PDF)
Live Science - Cephalopods: Facts about octopus, squid, nautilus and more
PNAS - Symbiotic organs shaped by distinct modes of genome evolution in cephalopods
Smithsonian Ocean - Cephalopods: Octopus and Squids

cephalopod

class of mollusks

Also known as: Cephalopoda, Siphonopoda

Written by

Clyde F.E. Roper

Curator of Mollusca, Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. Coauthor of Cephalopods of the World.

Clyde F.E. RoperAll

Fact-checked by

Britannica Editors

Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....

Britannica Editors

Last updated

Oct. 16, 2026 •History

cephalopod, any member of the class Cephalopoda of the phylum Mollusca, a small group of highly advanced and organized, exclusively marine animals. The octopus, squid, cuttlefish, and chambered nautilus are familiar representatives. The extinct forms outnumber the living, the class having attained great diversity in late Paleozoic and Mesozoic times. The extinct cephalopods are the ammonites, belemnites, and nautiloids, except for five living species of Nautilus. The cephalopods agree with the rest of the Mollusca...

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