An organic-walled dinoflagellate cyst, Operculodinium aguinawense sp. nov. is described from recent marine sediments in Biafra Bay, Gulf of Guinea, Atlantic Ocean. This species is characterized by a subspheroidal, egg-shaped cyst body with a fibroreticulate surface wall, and flexible to stout processes with wide, fibrous bases and multifurcate terminations. Paratabulation is only expressed by the loss of a single precingular paraplate (3″). The distribution of this form in recent marine sediments suggests an affinity for lower salinity conditions (29) and as such, it could be an index of paleosalinity changes. Marine palynomorph records from the Gulf of Guinea document its occurrence from at least the Last Interglacial. Fluctuations in abundance appear to be associated with periods of strengthened monsoon dynamics and river discharge.