Instead, some eukaryotes have obtained them from others through
secondary endosymbiosis or ingestion.
Secondary endosymbiosis occurs when the product of primary endosymbiosis is itself engulfed and retained by another free living eukaryote.
The process of
secondary endosymbiosis left its evolutionary signature within the unique topography of plastid membranes.
Chlorarachniophytes are particularly interesting study objects, because these microbes still retain some of the green alga's nucleus, suggesting that the process of
secondary endosymbiosis is still ongoing.
Eons later, in a process called
secondary endosymbiosis, predatory protozoa gulped down the green algae.