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
European sea sturgeon 19th century, these fish were used extensively to produce caviar, but have been a protected species in Europe since 1982. European sea sturgeon The European sea sturgeon ("Acipenser sturio"), also known as the Atlantic sturgeon or common sturgeon, is a species of sturgeon previously found on most coasts of Europe. It is anadromous and breeds in rivers. It is currently a critically endangered species. Although the name Baltic sturgeon sometimes has been used, it has now been established that sturgeon of the Baltic region are "A. oxyrinchus", a species otherwise restricted to the Atlantic coast of North America. The wedge-shaped