Complex sentence: There are two genera, the uninucleate "Actinophrys" and the multinucleate "Actinosphaerium", comprising the most frequently found freshwater heliozoa.
Split into simpler sentences: There are two genera, the uninucleate "Actinophrys" and the multinucleate "Actinosphaerium". These include the most frequently found freshwater heliozoa.