Theodoxus fluviatilis is considered holarctic, occurring in both the Nearctic and Palearctic biogeographic regions. However, they are more commonly seen in the Palearctic region, spreading far west to England, and east into southwestern Asia. Many patches within Europe are uninhabited, mainly the mountainous regions. This snail's ability to survive in freshwater allowed for migration throughout Eastern Europe, and later re-entry into the brackish waters of the Baltic Sea.
Biogeographic Regions: nearctic (Introduced ); palearctic (Native )
Other Geographic Terms: holarctic