Prochloron

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. However this theory is largely refuted by phylogenetic studies which indicate Prochloron is not on the same line of descent that lead to chloroplast-containing algae and land plants.