Common Northern European Opossum Shrimp

<em>Mysis relicta</em>, the common northern European opossum shrimp, is a small mysid crustacean in the family Mysidae, found in cold freshwater lakes and brackish coastal environments across northern Europe and North America. The species is a glacial relict — populations became isolated in deep, cold lakes following the retreat of glaciers at the end of the last Ice Age. <em>Mysis relicta</em> typically inhabits the cool profundal and sublittoral zones of oligotrophic lakes, undertaking diel vertical migrations to feed on phytoplankton, zooplankton, and organic detritus in shallower waters at night. Its geographic range includes lake systems in Denmark, Norway, Sweden, and the United States, particularly in Scandinavia and the Great Lakes region. The species has not been formally evaluated under the IUCN Red List framework. Biological traits such as lifespan, body size, and diet remain poorly documented at a standardized population level for this species. <em>Mysis relicta</em> is ecologically significant as a prey item for fish species including lake trout and Arctic char, and as an important link in the pelagic food webs of cold northern lakes.