crustacean

Introduction
General features
- Size range and diversity of structure
- Distribution and abundance
- Importance to humans
Natural history
- Reproduction and life cycles
- Ecology
Form and function of external features
- General features
- Appendages
- Exoskeleton
Form and function of internal features
- The nervous system
- The digestive system
- The excretory system
- The respiratory system
- The circulatory system
- Hormones
Evolution and paleontology
Classification
- Distinguishing taxonomic features
- Annotated classification
- Critical appraisal

References & Edit History Quick Facts & Related Topics

Images

Diagram of the tree of life based on the three-domain system, showing Archaea, Bacteria, and Eukaryota branching into four kingdoms: Plants, Animals, Fungi, and Protista, with illustrations of representative organisms for each group.

At a Glance

crustacean 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 crustacean appendages adapted for sensing, feeding, swimming, and walking?
How do crab larvae develop from zoea to megalopa to adult form?
How do crabs influence the evolution of mollusk shells?
How do crabs walk sideways?
How do crustacean bodies form segments and specialized appendages?
How do crustaceans differ from insects, spiders, and centipedes?
How do crustaceans survive in freshwater, seawater, and highly salty inland brines?
How do crustaceans survive in high Arctic regions?
How do decapods breathe in water and on land?
How do dwarf male barnacles reproduce with larger individuals?
How do hermit crabs choose shells for protection?
How do male and female crustaceans differ in size and body structures?
How do planktonic crustaceans support fish, seabirds, and whales?
How do shrimp and lobsters swim backward rapidly?
How does a barnacle change from a swimming cyprid larva into an attached adult?
How does a crustacean carapace protect the body and gills?
How does a nauplius larva differ from an adult crustacean?
How does the crustacean exoskeleton provide protection and support?
How large can Japanese spider crabs grow?
How small can water fleas and copepods be?
What are photophores in some ocean shrimp used for?
What happens during the stages of crustacean molting?
Where do crustaceans live around the world?
Which animals are included in the decapod order?
Which animals belong to the crustacean group?
Which body features identify an animal as a crustacean?
Which crustaceans can reproduce without fertilization?
Which crustaceans have a carapace?
Which crustaceans live as parasites on other aquatic animals?
Which crustaceans live at the greatest depths of the ocean?
Which materials make crustacean exoskeletons hard?
Why are copepods and krill important in ocean food webs?
Why are decapods called ten-legged crustaceans?
Why are newly molted crabs called soft-shell crabs?
Why do crustaceans have two pairs of antennae?
Why do male crabs and lobsters often have larger pincers than females?
Why do some crustaceans have clamlike shells with two valves?
Why must crustaceans molt as they grow?
Why must land crabs return to water when their larvae hatch?

Science Insects & Other Invertebrates Crustaceans

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External Websites

Te Ara ï¿½ The Encyclopedia of New Zealand - Crabs, crayfish and other crustaceans
The Canadian Encyclopedia - Crustacean
The Royal Society Publishing - Interface Focus - Structural diversity of crustacean exoskeletons and its implications for biomimetics
National Center for Biotechnology Information - PubMed Central - Effects of Organotins on Crustaceans: Update and Perspectives
ABC listen - Off Track - Spineless swimmers and crawling crustaceans

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

crustacean - Children's Encyclopedia (Ages 8-11)
crustacean - Student Encyclopedia (Ages 11 and up)

crustacean

arthropod

Also known as: Crustacea

Written by

James Green

Emeritus Professor of Zoology, Queen Mary and Westfield College, University of London. Author of The Biology of Estuarine Animals.

James GreenAll

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. 14, 2026 •History

crustacean, any member of the subphylum Crustacea (phylum Arthropoda), a group of invertebrate animals consisting of some 45,000 species distributed worldwide. Crabs, lobsters, shrimps, and wood lice are among the best-known crustaceans, but the group also includes an enormous variety of other forms without popular names. Crustaceans are generally aquatic and differ from other arthropods in having two pairs of appendages (antennules and antennae) in front of the mouth and paired appendages near the mouth...

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