Anatomy.
![Picture](/uploads/1/3/9/7/13974932/9159849.jpg)
Arthropods are triploblast which means they have three tissue layers. They are coelomates and they have bilateral symmetry. They contain an exoskeleton, which is made of chitin that is sometimes reinforced with calcium carbonate. They also have segmented bodies, get their names from their jointed appendages. They may be legs, arms, antennae, mouth-parts, or reproductive organs.