Darkfield and polarised light micrograph of a common freshwater shrimp (Gammarus pulex). This freshwater amphipod crustacean is found in streams, rivers, and other aquatic habitats throughout Europe and northern Asia. It is an important part of the food chain in freshwater ecosystems, serving as a food source for a variety of fish, birds, and other aquatic organisms. G. pulex has a flattened body with a curved shape. It has a hard exoskeleton and jointed legs, which allow it to move and swim in the water. The body is typically brown or green in colour, with a mottled appearance that provides camouflage in its natural habitat. It is a detritivore, which means that it feeds on decaying organic matter, including plant material and dead animals. It is also an opportunistic feeder and will consume a variety of other food sources, including algae, aquatic insects, and small fish. In addition to its ecological role as a food source, G. pulex is also used as a bioindicator species for monitoring the health of freshwater ecosystems. It is sensitive to changes in water quality, including the presence of pollutants such as heavy metals and pesticides, and can be used as an early warning system for detecting changes in the environment.