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
Geography of the European Union the dichotomy between highland and mountainous Southern Europe and a vast, partially underwater, northern plain ranging from United Kingdom in the west to Poland in the east. These two halves are separated by the mountain chains of Pyrenees and Alps/Carpathians. The northern plains are delimited in the west by the Scandinavian mountains and the mountainous parts of the British Isles. Major shallow water bodies submerging parts of the northern plains are the Celtic Sea, the North Sea, the Baltic Sea complex, and the Barents Sea. The northern plain contains the old geological continent of Baltica, and so may be regarded