Amphipods are small crustaceans that are found in both marine and freshwater habitats all around the world. They are also known as "scuds", "sideswimmers" or "hoppers". These names reflect the unique characteristics of the amphipod's behavior - they move by quickly swimming or hopping sideways. Other synonyms for "amphipod" include "freshwater shrimp", "sand flea" and "bay shrimp". These creatures are important species for eco-systems as they are a food source for fish, birds and larger invertebrates. Scientists have discovered over 10,000 different species of amphipods all living in different environments. Despite their small size, amphipods are important animals in their respective habitats, and serve as indicators of the health of the environment.