Cryptophyceae and rhodophyceae; chemotaxonomy, phylogeny, and application

It is postulated that the primary endosymbiosis of a photosynthetic n − 3 C18 PUFA-producing prokaryotic cyanobacteria and a eukaryotic host capable of chain elongation and desaturation of exogenous PUFA, resulted in the Rhodophyceae capable of producing n − 3 C20 PUFA. The secondary endosymbiosis of a photosynthetic C20 PUFA-producing eukaryote (a rhodophyte) and a eukaryotic host capable of further chain elongation and desaturation, resulted in the Cryptophyceae, capable of producing both n − 3 C20 and C22 PUFA de novo.