Crabs and Crayfish (Decapoda) are found worldwide. The oldest records of crayfish near Australia are 115 million years old. This order of scavenger crustaceans also includes lobsters, prawns and shrimp. All have 10 legs and the ability to swim and walk (sometimes sideways). Depending on the species, they can live in fresh or salt water. They spend much of their time grooming to prevent particulate build up on their legs and bodies. As their bodies grow they will continue to molt their hard outer shell exoskeletons. As scavengers they feed on live and dead fish and plants. All over the world crabs and crayfish are used as food, bait, and also pets in aquariums.