The Order Amphipoda is a group of small, laterally compressed crustaceans commonly found in marine, freshwater, and some terrestrial environments. Amphipods, often called scuds or sand hoppers, have segmented bodies with distinct head, thorax, and abdomen regions, and they lack a carapace. They typically possess multiple pairs of legs adapted for swimming, crawling, or burrowing, and many species are detritivores, scavenging organic matter and contributing to nutrient cycling in ecosystems. Amphipods play an important role in aquatic food webs as a food source for fish, birds, and other invertebrates, and some species are used as bioindicators to assess water quality and environmental health.