SUMMARYDictyocha fibulawas cultured in an enriched seawater medium from collections taken at Edmonds, Washington. The optimum temperature for growth is 10 C at salinity 24% and 160 ft‐c illumination in Provasoli enriched seawater at the concentration of 7.5 ml/liter seawater. Average generation time is 49 hr. In addition to swimming cells with skeletons, swimming cells without skeletons and nonswimming coenocytes were observed in clonal cultures at 15