There are two main genera of Actinophryids. Actinophrys has a single central nucleus, with a body typically around 50 μm in diameter and pseudopods around 100 μm long. Actinosphaerum is several times larger and multinucleate, and is found exclusively in fresh water. A third genera, Echinosphaerum, has been described but may be equivalent to Actinosphaerum.
Under unfavorable conditions, the cell will form a cyst, which is multi-walled and covered in spikes. Sexual reproduction occurs through a process of autogamy (self-fertilization) inside of the cyst: the cell undergoes meiosis and divides in two, then fuses back together. Otherwise reproduction is usually by binary fission.