Add to ORKGNational audienceThe recurrent detection of parasitic zoospores among aquatic heterotrophic flagellates has recently changed our view of how the microbial loop is organized, and has called into question the role of eukaryotic parasites in the aquatic food web. The Perkinsozoa group, already known to play a significant role as parasite in marine systems, is of special interest here, since it has recently been detected in several lakes by molecular methods (sequencing of clones libraries). In marine systems, this group is known to comprise only intracellular parasites of molluscs or phytoplanktonic species, but their hosts in freshwater environments are still unknown, and little is yet known about their functional importance in planktonic sys...