Gymnosphaeridae

Heliozoa with axonemes arising from a central homogeneous axoplast, microtubules in axoneme arranged in irregular hexagonal prisms. One eccentric or multiple nuclei, mitochondrial cristae are tubular, and different types of extrusomes. Usually attached to the substrate by a cytoplasmic stalk with the cell body differentiated into a 'head' with radiating axopodia, and an extensive multinucleate amoeboid base. The stalk of Actinocoryne is contractile. May occasionally be free-swimming. Cell surface may be covered by tangential siliceous (?) spicules, mucus, or be naked. Life cycle is complex but not fully resolved. Actinocoryne may undergo multiply budding from 'head' to produce small, temporary floating spherical amoeboid cells. Motile cells with two flagella are produced by Gymnosphaera and Actinocoryne (possibly with an annual cycle), marine.