''Prochloron'' (from the Greek ''pro'' (before) and the Greek ''chloros'' (green) ) is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea squirts). Part of the phylum

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

, 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 In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

studies which indicate ''Prochloron'' is not on the same line of descent that lead to chloroplast-containing algae and land plants. ''Prochloron'' was discovered in 1975 by Ralph A. Lewin of the Scripps Institution of Oceanography. ''Prochloron'' is one of three known prochlorophytes, cyanobacteria that contain both chlorophyll ''a'' and ''b'' bound to a special light-harvesting protein. Surprisingly, unlike most cyanobacteria ''Prochloron'' do not contain the red or blue pigments called phycobilins, seen in many species of cyanobacteria. Repeated unsuccessful attempts to culture ''Prochloron'' outside a host make them the only known obligate photosymbionts in the phylum

Chordata A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (Apomorphy and synapomorphy, synapomorphies) th ...

. Strictly speaking the name "''Prochloron''" was not validly published under either ICNP or

ICNafp The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all th ...

. The two codes do each have a valid version of the genus: * ''Prochloron'' , valid under

* ''Prochloron'' , valid under ICNP by being published in '' Int. J. Syst. Bacteriol.''

Species

The only taxonomically valid species is ''P. didemni''. Again there is a version in each of the two ''Codes''.

References

* * Waterbury, John, et al. Little Things Matter A Lot. Oceanus Magazine. 2004, 43(2). * Synechococcales Cyanobacteria genera {{cyanobacteria-stub