Fauna of Europe of the Baltic Sea has led to the evolution of many slightly divergent species, such as the Baltic Sea herring, which is a smaller variant of the Atlantic herring. The most frequent benthic species are "Saduria entomon" and "Monoporeia affinis", which is originally a freshwater species. A great part of its bottom is anoxic and without animal life. The Baltic Sea and North Sea are also home to a variety of marine mammals (common seals, grey seals). Europe contains several important freshwater ecoregions, including the heavily developed rivers of Europe, the rivers of Russia, which flow into the Arctic, Baltic,
Geology of the North Sea in the West, just North of the Netherlands. A larger graben is found in the subsurface below the Skagerrak, this north-south structure is called the Bamble-Oslo Graben. The Viking Graben is separated from the Faeroe Shetland Basin below the Atlantic by the Shetland Platform, the two structures join in the area north-east of the Shetland Islands. The area we now call the North Sea was interspersed amid several separate continental areas (Siberia, Baltica, Gondwana, and Laurentia) as well as the Iapetus Ocean and Tornquist Sea. Plate tectonics and continental collisions (orogenies) brought the features together of the North Sea that