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Science & Nature • Marine Biology

Crustacean

Crustaceans are a subphylum of arthropods that includes animals such as crabs, lobsters, shrimp, crayfish, barnacles, and woodlice.

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

Crustaceans are a subphylum of arthropods that includes animals such as crabs, lobsters, shrimp, crayfish, barnacles, and woodlice. They are mostly aquatic, with many species living in marine and freshwater habitats, and they are characterized by an exoskeleton, jointed appendages, and antennae.

Classification

Crustaceans are arthropods traditionally classified in the subphylum Crustacea. Sources vary on the exact number of described species, but estimates in the provided sources range from about 31,300 to 45,000.

Anatomy and traits

Crustaceans generally have a hard exoskeleton, segmented bodies, jointed appendages, and two pairs of antennae. Growth requires molting, because the exoskeleton does not expand with the animal.

Habitat and diversity

Most crustaceans live in aquatic environments, especially the sea, but some species inhabit freshwater or terrestrial environments. The group includes very small planktonic species as well as large crabs such as the Japanese spider crab.

Ecological importance

Crustaceans are major components of marine and freshwater ecosystems. They contribute to plankton communities, benthic food webs, and the diets of many fish, birds, and marine mammals. In Canada, crustaceans are significant in marine and freshwater ecosystems and in Canadian fisheries, especially species such as lobster, crab, shrimp, and crayfish.

Key facts

  • Crustaceans belong to the arthropod phylum and are usually treated as the subphylum Crustacea.
  • Most crustaceans are aquatic, especially marine species, though some live on land.
  • They have a hard exoskeleton that must be molted for growth.
  • Crustaceans are an important part of aquatic food webs and plankton communities.
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Canadian context

Crustaceans are significant in Canada’s marine and freshwater ecosystems and in Canadian fisheries, especially species such as lobster, crab, shrimp, and crayfish.

Frequently asked questions

What is a crustacean?
A crustacean is an arthropod in the subphylum Crustacea, usually with a hard exoskeleton, jointed limbs, and two pairs of antennae.
Are crustaceans fish?
No. Crustaceans are invertebrate arthropods, not fish.
What animals are crustaceans?
Crabs, lobsters, shrimp, crayfish, barnacles, woodlice, water fleas, and many other species are crustaceans.
Where do crustaceans live?
Most live in water, especially marine habitats, but some species live in freshwater or on land.
How do crustaceans grow?
They grow by moulting, shedding their exoskeleton and forming a new one.

References

  1. The Canadian Encyclopedia — https://thecanadianencyclopedia.ca/en/article/crustacean
    Supports: Definition, anatomy, habitat range, and species diversity of crustaceans.
  2. Britannica — https://www.britannica.com/animal/crustacean?anchor=ref409648
    Supports: Classification, worldwide diversity, aquatic habit, and distinguishing features such as antennae and mouth appendages.
  3. Simple English Wikipedia — https://simple.wikipedia.org/wiki/Crustacean
    Supports: Examples of crustaceans and approximate number of described species.
  4. Encyclopedia of Life — https://eol.org/docs/discover/crustaceans
    Supports: General characteristics, body structure, marine ecological importance, and examples of crustacean groups.