They are free-swimming, solitary cells resembling Euglena, enclosed in species-specific envelopes that range in shape from spherical to elongated, initially smooth and colorless but later becoming brown, brittle, and ornamented with iron and manganese salts. They possess a sharply defined neck or collar around an apical pore from which a long locomotory flagellum emerges. They are green and photosynthetic, with various types of chloroplasts, while some are colorless and osmotrophic. They inhabit freshwater environments, typically acidic to neutral, including peaty pools rich in iron and manganese, and are widely distributed globally.