Actinosphaerium (act-in-o-sphere-ee-um) (=Echinosphaerium), one of the largest freshwater heliozoa, may measure up to 500 microns, often with outer layer being very vacuolated. Multiple nuclei and nucleating sites for the arms line at the interface between the inner and outer regions of cytoplasm. Yellowy zone in the centre is some food being digested - these heliozoa can consume small metazoa. Dark ground illumination.