Arthropods make up over 75% of the world's animal species. Arthropods
include animals such as insects, crustaceans and arachnids.
The largest group of Arthropods are the insects. The next largest group
are the crustaceans, including lobsters and crabs. The arachnids include
spiders and ticks.
Other Arthropods include centipedes and millipedes.
Arthropods have limbs with joints that allow them to move. They also
have an exoskeleton, which is a hard, external skeleton. Their body cavity
contains the nervous system, circulatory system, reproductive system and
digestive system.