Ponto-Caspian Species Hypania invalida (Grube, 1860) (Polychaeta, Ampharetidae) in the Inland Waters of Europe: Modern Distribution and the Paleorefugium Hypothesis

The paper deals with the state of research on the distribution of the invasive brackish-water Ponto-Caspian species of Polychaeta <i>Hypania invalida</i> (Grube, 1860) in water bodies of Europe. In the native (historical) area of its distribution covering the lower reaches of the Danube, Dnieper, and Volga rivers, the populations of this representative of Polychaeta are known from hydrobiological studies of the late 19<sup>th</sup> and early 20<sup>th</sup> centuries. The main biotopes of its localization are deposits of gray silt, silted sand, and silts with impurities of mollusk shells. After the creation of cascades of reservoirs on the Dnieper and Volga rivers, against the background of increased mineralization of water masses, in the 1970s and 1980s, the spread of <i>H. invalida</i> from the lower to the middle reaches of these rivers was recorded. In the middle and upper reaches of the Danube River, the settlements of <i>H. invalida</i> have been known since the 1930s. The article analyzes data on the findings of <i>H. invalida </i>populations in many rivers and canals of the Central and Western Europe, especially numerous - from the publications of the beginning of the 21<sup>st</sup> century. Most scientists believe that this Polychaeta species spread is facilitated by active logistics in the water network of the region. The paper considers the hypothesis of <i>H. invalida</i> spread in the inland waters of the Central and Western Europe from relict sites in the upper reaches of the Pra-Danube River, which were formed at the end of the Holocene epoch 11-13 thousand years ago after the significant increase in salinity of the waters of the Pontic Sea (the Ancient Black Sea) basin and the migration of the oligo- and mesohaline invertebrate species to the upper reaches of the river.