The ultrastructure of apical cells of six species of Sphacelaria (S. arctica, S. cirrosa, S. nana, S. racemosa, S. radicans, and S. rigidula) is studied here. In most details such as ultrastructure of chloroplasts, mitochondria, microbodies, nuclei and centrioles all Sphacelaria species studied are similar. Only in sections of S. rigidula, however, do pyrenoid-like structures occur.