Prymnesium parvum is a haptophyte, belonging to Haptophyta (=Prymnesiophyta). The species is of concern because of its ability to produce a toxin, prymnesin. It is a flagellated alga that is normally found suspended in the water column. It was first identified in North America in 1985 and it is not known if it was introduced artificially (e.g., an invasive species of missed in previous surveys). Toxin production mainly kills fish and appears to have little effect on cattle or humans. This distinguishes it from red tide, which are algal blooms whose toxins lead to harmful effects in people. Although no harmful effects are known, it is recommended not to consume dead or dying fish exposed to a P. parvum bloom. Prymnesium parvum of Haptophyta is sometimes termed a golden alga or a golden brown algae as is Chrysophyceae of Heterokontophyta but the taxonomy of algae is under complex revision leading to contradictions in terms especially in non scholarly texts such as those from state wildlife departments.

 

Edited from wikipedia: Prymnesium parvum