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
History of the North Sea mixing with the native Celtic populations. The Viking Age began in 793 and for the next two centuries the Vikings ruled the North Sea. From the Middle Ages until the end of the 15th century, before the development of good roads, maritime trade on the North Sea connected the economies of northern Europe, Britain, and Scandinavia with each other as well as with the Baltic and the Mediterranean. The Netherland low countries and German speaking lands were the central hub for English Channel and North Sea coastal trade and organizations such as the Hanseatic League, aimed at protecting interests of