Latitudinal distribution of freshwater sponge species across European Russia

This study provides original faunistic data on freshwater sponge dispersal across a huge territory of European Russia from north to south, highlighting the northern limits of thermophilic and north-adapted species. The holarctic species Ephydatia muelleri and, especially, Spongilla lacustris were predominant in northern areas, while the cosmopolitan Ephydatia fluviatilis and Eunapius fragilis were less prevalent. Moving to the south, E. fluviatilis took the lead. The distributional pattern of northern sponges aligns with literature data from North Europe, confirming the prevalence of the holarctic species in high latitudes. Tubella (=Trochospongilla) horrida, Eunapius carteri, and Radiospongilla cerebellata are considered to be thermophilic species that could not tolerate the conditions in northern regions. Notable findings include the extension of Eunapius carteri's known range and the first report of R. cerebellata within Russia, which is also the second record for Europe. Three potentially expected species were not found in the studied area, indicating regional rarity. We also provide molecular and morphological evidence for the synonymy of Spongilla arctica and Spongilla lacustris. Finally, we discuss the impacts of climate change and agricultural activities on northern and southern sponge habitats respectively.