[3] Golden algae is also commonly used to refer to a single species, Prymnesium parvum, which causes fish kills.

Originally they were taken to include all such forms of the diatoms and multicellular brown algae, but since then they have been divided into several different groups (e.g., Haptophyceae,[5] Synurophyceae) based on pigmentation and cell structure.

They are now usually restricted to a core group of closely related forms, distinguished primarily by the structure of the flagella in motile cells, also treated as an order Chromulinales.

An important characteristic used to identify members of the class Chrysophyceae is the presence of a siliceous cyst that is formed endogenously.

[citation needed] Because many of these organisms had a silica capsule, they have a relatively complete fossil record, allowing modern biologists to confirm that they are, in fact, not derived from cyanobacteria, but rather an ancestor that did not possess the capability to photosynthesize.