All arthropods have an external skeleton called an exoskeleton.

Some of the exoskeleton functions are:

  • It provides structural support.
  • It protects the body.
  • It facilitates muscle attachment and movement.

Crabs, lobsters and scorpions are arthropods.

The arthropods
Source | Happy Learning English

What is an Arthropod? – Dan Babbitt
These are the five major groups of arthropods:
insects, arachnids, crustaceans, millipedes and centipedes.
Source | Smithsonian Education