arthropod

Introduction & Top Questions
General features
- Size range
- Distribution and abundance
- Importance
Form and function
- The exoskeleton and molting
- Muscles, appendages, and locomotion
- Digestive system and feeding
- Respiratory system
- Circulatory system
- Excretory system and water balance
- Nervous system and organs of sensation
- Reproductive system and life cycle
Evolution and paleontology
Classification
- Distinguishing taxonomic features
- Annotated classification
- Critical appraisal

References & Edit History Quick Facts & Related Topics

Images, Videos & Interactives

A spiny lobster (Palinurus elephas) with long, striped antennae and spiny body stands on sandy ground near a rocky crevice underwater.

A large Scolopendra centipede with a dark segmented body and yellow legs crawls across rough brown wood.

Horseshoe crab (Limulus polyphemus) with a hard, rounded shell and long pointed tail lying on sandy ground.

Illustration showing a variety of adult insects, each labeled with its common name and order, including walkingstick, earwig, stonefly, tree cricket, dragonfly, female scale, cat flea, thrips, sucking louse, thysanuran, ant, scarab beetle, stinkbug, mosquito, and cabbage butterfly, highlighting their diverse shapes and sizes.

At a Glance

arthropod 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

Green tree python snake (Chondropython viridis) in a rainforest.

Creepy Crawlers Quiz

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

Animal Factoids

Related Questions

How are centipedes different from millipedes?
How are insect wings built from the exoskeleton?
How are insects different from arachnids?
How are spiders different from insects?
How do ants and bees develop different worker and reproductive castes?
How do chelicerae help spiders capture and eat prey?
How do crustacean larvae differ from adult crustaceans?
How do flexible joints allow arthropods to move despite having hard exoskeletons?
How do nymphs differ from adult grasshoppers and true bugs?
How do soil arthropods help form humus from dead leaves and wood?
How do spider pedipalps function in feeding and reproduction?
How do spiders regenerate a lost leg?
How do waxy layers in the exoskeleton help land arthropods avoid drying out?
How does an arthropod form a new exoskeleton after molting?
How does chitin help make an arthropod’s exoskeleton strong?
How does ecdysone trigger molting in arthropods?
How does juvenile hormone affect an insect’s metamorphosis?
How have crayfish and pill bugs adapted to freshwater and life on land?
How many pairs of legs do insects usually have?
When did trilobites live, and when did they become extinct?
When do the first arthropod fossils appear in the geologic record?
Where do myriapods such as centipedes and millipedes commonly live?
Which animals belong to the Chelicerata subphylum?
Which animals belong to the Crustacea subphylum?
Which animals belong to the Hexapoda subphylum?
Which animals belong to the Myriapoda subphylum?
Which arthropods are used as food by people around the world?
Which body features distinguish arthropods from other invertebrate animals?
Which diseases can ticks transmit to people?
Which four living subphyla make up the phylum Arthropoda?
Why are copepods and krill important in ocean food chains?
Why can planktonic crustacean larvae help a species spread to new places?
Why can some marine arthropods grow larger than land arthropods?
Why did flight help insects become such a diverse group of land animals?
Why do arthropods need to molt as they grow?
Why do caterpillars and adult butterflies often eat different foods?
Why do chelicerates such as spiders and scorpions lack antennae?
Why does an arthropod exoskeleton limit the maximum size of animals living on land?
Why is an arthropod especially vulnerable immediately after shedding its exoskeleton?
What is an arthropod?
What are the main characteristics of arthropods?
What are the major groups of arthropods?
What is a spider?
How are spiders different from insects?
Are all spiders venomous?
How long do spiders live?

Science Insects & Other Invertebrates Arthropods

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External Websites

Arizona-Sonora Desert Museum - A Vertebrate Looks at Arthropods
The Canadian Encyclopedia - Arthropoda
University of Central Florida Pressbooks - General Biology - Phylum Arthropoda (in Superphylm Ecdysozoa)
National Center for Biotechnology Information - Arthropoda
NC State University - General Entomology - The Arthropods
San Diego Zoo Animals and Plants - Arthropods
Animal Diversity Web - Arthropod
UC Museum of Paleontology Understanding Evolution - The Arthropod Story
University of Hawaii - Exploring Our Fluid Earth - Phylum Arthropoda
Animal Corner - What is an Arthropods?

Britannica Websites

Articles from Britannica Encyclopedias for elementary and high school students.

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

arthropod

animal phylum

Also known as: Arthropoda

Written by

Robert D. Barnes

Professor of Biology, Gettysburg College, Pennsylvania, 1963–93. Author of Invertebrate Zoology.

Robert D. Barnes

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

Sep. 18, 2026 •History

arthropod, (phylum Arthropoda), any member of the phylum Arthropoda, the largest phylum in the animal kingdom, which includes such familiar forms as lobsters, crabs, spiders, mites, insects, centipedes, and millipedes. Of the nearly 1.8 million animal species that have been described by science, about 84 percent are arthropods. Arthropods are represented in every habitat on Earth and show a great variety of adaptations. Several types live in aquatic environments, and others reside in terrestrial ones;...

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