Heliozoa

Heliozoa, commonly called sun-animalcules, are microbial eukaryotes (protists) whose spherical bodies bear stiff arms called axopodia that radiate outward like rays. These microtubule-supported projections are used to catch food, to sense the surroundings, to move and to attach. Heliozoa resemble the Radiolaria but lack a central capsule and complex skeletal elements, although some make simple scales and spines, and they live in both freshwater and marine environments. The name was once used for a formal class or phylum, but the group is now understood to be polyphyletic: its orders do not share a single common ancestor and instead evolved axopodial arms independently. The orders are scattered across the eukaryote tree, with Actinophryida among the Stramenopiles, Centroplasthelida in Haptista, Desmothoracida and Gymnosphaerida in Cercozoa, Taxopodida among the Radiolaria and Microhelida in Pancryptista. Heliozoa therefore survives mainly as a descriptive term for a body plan. Cavalier-Smith proposed keeping it as a narrower formal taxon from 2012, but that definition never won consensus.