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,
Mediterranean mussel edulis" and "Mytilus trossulus", when they are found in the same locality. "M. galloprovincialis" is considered the most warm-water-tolerant species of the three, and has the most southerly distribution in Europe and North America. In Europe, "Mytilus galloprovincialis" is found in the Mediterranean Sea and the Black Sea, and on the Atlantic coasts, in Portugal, north to France and the British Isles and Norway. Recently this species has also been found in the European Arctic including northern Norway and Svalbard In the northern Pacific the species is found along the coast of California, where it was introduced from Europe by