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
Geology of the Baltic Sea wells have revealed the existence of petroleum of Lower Paleozoic age beneath Gotland. Bibliography Geology of the Baltic Sea The Geology of the Baltic Sea is characterized by having areas located both at the Baltic Shield of the East European Craton and the Danish-North German-Polish Caledonides. There is a distinction between what is the current Baltic Sea depression, formed in the Cenozoic Era, and the much older sedimentary basins whose sediments are preserved in the zone. Although glacial erosion has contributed to shape the present depression, the Baltic trough is largely a depression of tectonic origin that existed long before