| Protoperidinium obtusum (G. Karst.) Parke & J.D. Dodge, 1976 |
| Protoperidinium oceanicum (Vanhöffen) Balech, 1974 |
| Protoperidinium okamurai (T.H. Abé) Balech, 1974 |
| Protoperidinium orbiculare Paulsen, 1907 |
| Protoperidinium ovatum Pouchet, 1883 |
| Protoperidinium oviforme (P.A. Dang.) Balech, 1974 |
| Protoperidinium ovum (Schiller) Balech, 1974 |
| Protoperidinium pacificum (Kof. & J.R. Michener) F.J.R. Taylor & Balech ex Balech, 1988 |
| Protoperidinium pallidum (Ostenf.) Balech, 1973 |
| Protoperidinium pallidum var. daedalum Balech, 1978 |
| Protoperidinium paradoxum (F.J.R. Taylor) Balech, 1994 |
| Protoperidinium parapyriforme (Hermos.) Balech, 1974 |
| Protoperidinium parcum (Balech) Balech, 1974 |
| Protoperidinium parvicollum (Balech) Balech, 1973 |
| Protoperidinium parvispinum (Gaarder) Balech, 1974 |
| Protoperidinium parviventer Balech, 1978 |
| Protoperidinium pedunculatum (F. Schütt) Balech, 1974 |
| Protoperidinium pedunculatum var. pellucidum Bergh, 1881 ex Loeblich Jr. & Loeblich III, 1966 |
| Protoperidinium pedunculatum var. stellatum (Schiitt) Balech, 1974 |
| Protoperidinium pellucidum Bergh, 1882 |