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a subclass of protozoans of the class Sarcodina. The body is usually globose and has raylike appendages (pseudopodia) with dense protoplasmic axial filaments. Heliozoans include naked forms and forms having an external siliceous skeleton. There may be one or more nuclei. The majority of heliozoans are freshwater or marine planktonic organisms; some attach themselves to a substrate by means of a stalk. The protozoans feed on algae, protozoans, and rotifers; several individuals may combine to overcome larger prey. Heliozoans have contractile vacuoles. Reproduction is usually by binary fission. A sexual process has been observed in some species; the gametes resemble small adult individuals.