Cryptomonad flagellates, cells with a characteristic recurved posterior, imparting a sigmoid shape in lateral view. A keeled or winged rhizostyle extends the length of the cell acting as a cytoskeleton to maintain the cell shape. A simple furrow extends posteriorly from the vestibulum to a sac-like gullet. The periplast consists only of an inner sheet which is not associated with the cell membrane; a surface peri-plast component is lacking. The periplastidal compartment contains two chloroplasts, each with its own pyrenoid not transversed by thylakoids, and two nucleomorphs located near each pyrenoid. Chloroplasts posess Cr-phycoerythrin 566. Freshwater.