Actinophrys is a spherically symmetrical heliozoon, body 15 - 60 microns, with a large central nucleus with peripheral nucleolar material. Often with about 40-50 arms, the arms taper from base to tip. A layer of peripheral vacuoles may be present especially after feeding. The axonemes terminate on the nucleus. Several species are known, mostly occuring in freshwater. The type-species A. sol is the most widely reported freshwater heliozoon.