Actinosphaerium is a genus of heliozoa, amoeboid unicellular organisms with many axopodial filaments that radiate out of their cell.

Actinosphaerium species belong to an informal group known as heliozoa, which are unicellular eukaryotes (or protists) that are heterotrophic (also known as protozoa) and present slender, radiating, specialized pseudopodia known as axopodia.

Each axopodium is composed of a relatively stiff axial rod, surrounded by a thin layer of ectoplasm.

It has been observed consuming a diverse range of prey such as midge larvae, sessile colonial ciliates and several rotifer species.

[2] In 1965, Hovasse divided Actinosphaerium to create the genus Echinosphoerium or Echinosphaerium (both spellings were used in his work).