Gammarus varsoviensis Jazdzewski, 1975 (Amphipoda, Gammaridae): a long overlooked species in Ukrainian rivers.

The first findings of Gammarus varsoviensis in Ukraine are reported based on samples collected in 2009 and 2011. Until now, the species was known predominantly from the Baltic drainage area, with only one locality in the upper Pripyat River in Belarus (Black Sea basin). Our findings extend the known geographic range of this species ca. 830 kilometers south-east, revealing its occurrence in typically lowland streams and rivers of the Dnieper system, in the forest and Pontic steppe zone of the Black Sea basin. Based on the literature data we conclude that presence of this species in Ukraine was formerly overlooked through misidentification with morphologically close Gammarus lacustris. Based on such distribution pattern we can surmise that the species is native to the Black Sea drainage area. It could possibly have migrated to the Baltic basin through the Pripyat-Bug Canal, already in the XIX century. [ABSTRACT FROM AUTHOR]