Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,500 amphipod species so far described. They are mostly marine animals, but are found in almost all aquatic environments. Some 1900 species live in fresh water, and the order also includes terrestrial animals and sandhoppers such as Talitrus saltator.