This very large group of arthropods includes familiar animals such as shrimp, crabs, lobsters, crayfish, and barnacles. Like other arthropods, they have an exoskeleton which they must molt in order to grow. Crustaceans are distinct in their possession of two-parted (biramous) limbs and unique larval form. They are an important source of food for humans, with over 10 million tons being produced via farming and fishing every year. Most crustaceans are aquatic, though a few are adapted to a terrestrial lifestyle.