| Class | Genus | Species No. | Strain No. |
|---|---|---|---|
| Chrysophyceae | Ochromonas | 3 | 4 |
| Coccolithophyceae | Ochrosphaera | 2 | 3 |
| Bacillariophyceae | Odontella | 2 | 2 |
| Chlorophyceae | Oedogonium | 2 | 2 |
| Olisthodiscophyceae | Olisthodiscus | 2 | 3 |
| Ulvophyceae | Oltmannsiellopsis | 3 | 6 |
| Trebouxiophyceae | Oocystis | 3 | 5 |
| Chlorophyceae | Oogamochlamys | 1 | 2 |
| Coccolithophyceae | Oolithotus | 1 | 3 |
| Xanthophyceae | Ophiocytium | 3 | 4 |
| Cyanophyceae | Oscillatoria | 6 | 6 |
| Chlorophyceae | Ostravamonas | 1 | 2 |
| Mamiellophyceae | Ostreococcus | 3 | 4 |
| Dinophyceae | Ostreopsis | 1 | 1 |
| Imbricatea | Ovulinata | 1 | 1 |
| Oxyrrhea | Oxyrrhis | 1 | 2 |
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