The three distinct features Arthropods have is that they all have a bilateral symmetry, they have an open circulatory system and they have simple tubes.
An interesting arthropod I found was the praying mantis. It is an arthropod because its an insect, it has 6 legs, it has an exoskeleton and it is an invertebrate which means it has a backbone. The praying mantis also has a segmented body.