They differ from most others in that the mature cell is diploid and its nucleus does not show a dinokaryotic organization; also they show gametic meiosis.These cells are very large, from 1 to 2 millimetres in diameter, and are filled with large buoyant vacuoles. Some may contain symbiotic green algae, but there are no chloroplasts. Instead, they feed on other plankton, and there is usually a special tentacle involved in ingestion.