abstract:Prochloron (from the Greek pro (before) and the Greek chloros (green) ) is a unicellular oxygenic photosynthetic prokaryote commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea squirts). Part of the phylum cyanobacteria, it was theorized (endosymbiotic theory) that Prochloron is a predecessor of the photosynthetic components, chloroplasts, found in photosynthetic eukaryotic cells.