| Name | Children | Media (from resource) | Traits |
|---|---|---|---|
| Ulotrichales | 3 | 7 | 0 |
| Ulvophyceae | 2 | 19 | 0 |
| unclassified Diplostraca | 1 | 3 | 0 |
| unclassified Trebouxiophyceae | 1 | 2 | 0 |
| Unruhdinium penardii (Lemmermann) Gottschling 2017 | 0 | 1 | 0 |
| Urocentridae | 1 | 1 | 0 |
| Urocentrum Nitzsch ex Ersch & Gruber 1827 | 0 | 1 | 0 |
| Uroglena Ehrenberg 1834 | 0 | 9 | 0 |
| Uroglena volvox | 0 | 7 | 0 |
| Urostylida | 1 | 1 | 0 |
| Vaginicolidae | 10 | 46 | 0 |
| Vampyrella lateritia | 0 | 3 | 0 |
| Vampyrellida | 3 | 8 | 0 |
| Vampyrellidae (vampire amoebae) | 1 | 3 | 0 |
| Vannella simplex | 0 | 2 | 0 |
