Phylum Arthropoda

Includes: Crustaceans, Spiders, and Insects

Of the roughly one-and-a-quarter million named animals species, over one million are arthropods. They live in more habitats on earth than any other animal.

The name arthropod means ‘jointed foot.’ All arthropods have segmented bodies. A jointed protective armor, called an exoskeleton, covers the body. Think of a crab’s shell. Their body parts and muscles attach to the inside of this armor. An arthropod regularly sheds its exoskeleton to grow. Then expands its body before the new skeleton hardens. This process is called molting.

The incredible diversity and success of the arthropods is because of their very adaptable body plan. The evolution of many types of appendages—antennae, claws, wings, and mouthparts— allowed arthropods to occupy nearly every niche and habitat on earth.

For hundreds of millions of years, animals lived only in the oceans. Then, about 400 million years ago, fossil tracks suggest that an arthropod left the water to walk on land. Arthropods invaded land many times. Fossil evidence shows that different groups including insects, millipedes and centipedes, spiders, and scorpions all came ashore on their own at different times.


  • Hard exoskeleton made of chitin and protein
  • Possess numerous jointed appendages and a segmented body
  • Must molt to grow

Arthropod fact:

The fastest flying insects can travel at up to 35 miles per hour.

Word Bank

Segmented: the body is made up of a basic body compartment and the body gets bigger by adding more compartments. Like a classic train with its engine and caboose, segmented animals have repeating segments between specialized front and back compartments
Exoskeleton: means outside skeleton. A rigid, outside covering that provides structural support and gives muscles something to pull against
Appendage: parts added to the main body like claws and antennae
Chitin: a substance that provides a tough, protective covering; similar to keratin, the substance that human hair and nails are made from
Niche: the role or function of an organism in an ecosystem