Mysis is a genus of mysid crustaceans in the family Mysidae, distributed mainly in the coastal zone of the Arctic and high boreal seas.

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.

Mysis relicta is a freshwater species from boreal lakes of Northern Europe, also present in the Baltic Sea.

Mysis segerstralei is a fresh- and brackish-water species of the Eurasian and North American Arctic and sub-Arctic.

[4] This have led to theories that claim a natural lock system existed in the area during the Younger Dryas.