A warm-water flagellate; parasite of fish. Spironucleus vortens

Spironucleus vortens is a free living organism although it is also known as a fish parasite and the putative cause of hole-in-the-head disease of freshwater aquarium fish. Spironucleus vortens is another single-celled basal eukaryote like Giardia whose sequence can provide information on eukaryotic evolution.