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Description of ActinophryidaeCircumscription: One of several groups of organisms previously placed together as the heliozoa; round bodies with radiating stiff arms (axopodia); cell surface naked, no flagellated stage known. With one or many nuclei; siliceous plates or other siliceous aggregates form one layer of an encysted state. Affinities probably with the pedinellids, a group of stramenopiles. Ultrastructural identity: Mitochondria with bleblike (tubular) cristae. Axopodia supported by axonemes with microtubules in double polygonal spiral and nucleating on a nucleus or amorphous material. Two types of extrusomes: one larger homogeneous and osmiophilic, the other smaller and more heterogeneous. Dictyosomes typically associated with nuclei. Mitosis with microtubules penetrating from the cytoplasm, nuclear envelope mostly fragments. Synapomorphy: Tubulocristate protists with double polygonal spiral arrangement of microtubules in axopodia.