Within Europe, the highest species richness is found within the Mediterranean area, from the Iberian Peninsula to Greece. Areas of note with high levels of diversity include the limestone regions of the Mediterranean, the Alps and Carpathians, the ancient Balkan lakes and the rivers Danube, lower Dnieper and their tributaries.
The top five EU countries in terms of freshwater mollusc species richness (in descending order) are: France, Spain, Italy, Greece and Germany. However, Austria and Slovenia can be highlighted as holding an important number of species within a small area.
The majority of the freshwater mollusc species are endemic to Europe, with the areas of high endemism reflecting the areas of high species and subspecies diversity. Similar patterns of endemism are seen for both the Gastropods and the freshwater mussels, with an increase in endemism from north to south, and high levels of endemism throughout the Mediterranean zone.
The majority of the threatened freshwater molluscs are found within the Mediterranean zone, and the patterns follow closely the areas of endemism.