Arthropods are the largest category of animals on our planet; however, did you know that there are also marine arthropods? Crabs, shrimp and lobsters are some of them. They have the following two characteristics: "metamorphosis", which means that their body is divided into equal parts and "bilateral symmetry", which means that both sides of their body are uniform. Most marine arthropods have a hard skeleton on their external body. They have the ability to get rid of it, if they want to grow up, and a new one comes in its place. Scientifically, this process is called "extraction". One of the main reasons of this skeleton existence is to protect them from predators, such as sharks.