Skeletons on the Outside

Arthropods are soft on the inside and hard on the outside. There shell (skelleton) is waterproof. This is called an exoskeleton it protects the animal and it helps them
stay dry from evaporation. Water animals don't need to worry, but for animals on land this goes into effect. The first kind of speices to move out of water was the Arthropod and that is why Arthropods have shells. The material that the exoskeleton is made of is called a Chitin. The Chitin is made of long molecules that is made of smaller building blocks. Long chain molecules like these are calleds. When the Arthropods get older the exoskeleton dose'nt get bigger once the Arthropod out grows its shell they shed it off.