Heliozoa are typically spherical aquatic protozoa bearing thin, sensitive and dynamic cellular extensions known as axopods. The axopods are stiffened by bundles of unstable microtubules that radiate from the cell body in all directions. The skeleton, when present, consists of dispersed elements covering the cell surface. No fossils of Heliozoa have been reported.

Keywords: eukaryota; protozoa; actinopoda; radiozoa; microtubule‐based cytoskeleton

Figure 1.

Structure of two heliozoa: a centrohelid heliozoon (left) and the actinophryid species Actinophrys sol (right).



Corliss JO (1994) An interim utilitarian (‘user‐friendly’) hierarchical classification and characterization of the protists. Acta Protozoologica 33: 1–51.

Further Reading

Bardele CF (1977) Comparative study of axopodial microtubule patterns and possible mechanisms of pattern control in the centrohelidian heliozoa Acanthocystis, Raphidiophrys and Heterophrys. Journal of Cell Science 25: 205–232.

Cavalier‐Smith T (1993) Kingdom protozoa and its 18 phyla. Microbiological Reviews 57: 953–994.

Corliss (JO) (1994) An interim utilitarian (‘user‐friendly’) hierarchical classification and characterization of the protists. Acta Protozoologica 33: 1–51.

Febvre‐Chevalier C (1985) Class Heliozoa. In: Lee JJ, Hutner SH and Bovee EC (eds) An Illustrated Guide to the Protozoa, pp. 302–317. Lawrence, Kansas: Society of Protozoologists

Febvre‐Chevalier C, Bilbaut A, Febvre J and Bone Q (1989) Membrane excitability and motile responses in the Protozoa, with particular attention to the Heliozoan Actinocoryne contractilis. In: Anderson AV (ed.) Evolution of the First Nervous Systems. NATO ASI, Series A: Life Sciences, vol. 188, pp. 237–253. New York: Plenum Press.

Febvre‐Chevalier C (1990) Phylum Actinopoda, Class Heliozoa. In: Margulis L, Corliss JO, Melkonian M and Chapman D (eds) Handbook of Protoctista, pp. 347–362. Boston: Jones and Bartlett

Febvre‐Chevalier C and Febvre J (1992) Microtubule‐disassembly in vivo: intercalary destabilization and breakdown in the heliozoan Actinocoryne contractilis. Journal of Cell Biology 118: 586–594.

Febvre‐Chevalier C and Febvre J (1993) Structural and physiological basis of axopodial dynamics. Acta Protozoologica 32: 211–227.

Febvre‐Chevalier C and Febvre J (1994) Buoyancy and swimming in marine planktonic protists. In: Madcock L, Bone Q and Rayner MV (eds) Mechanics and Physiology of Animal Swimming, pp.13‐27. Cambridge: Cambridge University Press.

Patterson DJ and Hausmann K (1981) Feeding by Actinophrys sol (Protista, Heliozoa): 1 light microscopy. Microbios 31: 39–55.

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Febvre‐Chevalier, Colette, and Febvre, Jean(May 2001) Heliozoa. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0002103]