Mysis is a genus of mysid crustaceans in the family Mysidae, distributed mainly in the coastal zone of the Arctic and high boreal seas. Several species also inhabit northern freshwater lakes and the brackish Caspian Sea. Fifteen species are recognized. Body lengths range from 1 to 3 centimetres (0.4 to 1.2 in).The freshwater taxa of the genus have been referred to as "glacial relicts", and they comprise four closely related species, most of which also live in brackish water.