Baltic Sea as species in 2005 and 2018 respectively, having formerly been confused with more widespread relatives. The tiny Copenhagen cockle ("Parvicardium hauniense"), a rare mussel, is sometimes considered endemic, but has now been recorded in the Mediterranean. However, some consider non-Baltic records to be misidentifications of juvenile lagoon cockles ("Cerastoderma glaucum"). Several widespread marine species have distinctive subpopulations in the Baltic Sea adapted to the low salinity, such as the Baltic Sea forms of the Atlantic herring and lumpsucker, which are smaller than the widespread forms in the North Atlantic. A peculiar feature of the fauna is that it contains a
Parting of the Waters Creek waters flow either to the Atlantic Ocean via Atlantic Creek and the Yellowstone, Missouri and Mississippi Rivers, or to the Pacific Ocean via Pacific Creek and the Snake and Columbia Rivers. In the marshy area of Two Ocean Pass adjacent to Parting of the Waters, water actually covers the Continental Divide such that a fish could swim from the Pacific Ocean to the Atlantic Ocean drainages. In fact, it is thought that this was the pass that provided the route for Yellowstone cutthroat trout to migrate from the Snake River (Pacific) to Yellowstone River (Atlantic) drainages. This site received