Any of a class of freshwater protozoans .
They are sometimes considered relatives of heliozoans (organisms that for movement have extensions of cytoplasm called pseudopodia, but no flagella) because of their slender, radiating pseudopodia. The cores of the pseudopodia of some helioflagellates radiate from a central granule, as they do in some heliozoans. Helioflagellate life cycles alternate between flagellate and heliozoan phases. Some members are spherical, others oval.