A small group of
amoeboid protists with filose pseudopods and lacking shells, known mostly from soils and freshwater. They are distinguished from the similar
Vampyrellids by having
mitochondria with discoid rather than tubular cristae. The cells are usually small, up to about 50 μm in size. Some forms are naked, as
Nuclearia, a reddish parasite on algae; others have hollow silicaceous scales or spines, as
Rabdiophrys,
Pinaciophora,
Pinaciocystis, and
Pompholyxophrys, freshwater forms similar to heliozoa and formerly classified among them as the Rotosphaerids.