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chloroxybacteria (grass-green bacteria; prochlorophytes) Green-pigmented cyanobacteria that resemble the chloroplasts found as organelles in green plants and green algae. Like chloroplasts, chloroxybacteria perform photosynthesis using both chlorophylls a and b and carotenoids as pigments, and they lack phycobiliprotein accessory pigments (found in most cyanobacteria). The first to be discovered, in the 1960s, was Prochloron, a spherical (coccoid) cyanobacterium that lives as a symbiont on the surface or inside the cloaca of certain tunicates. Others include the filamentous Prochlorothrix, found free living in certain lakes. It is thought that the chloroxybacteria may share a common ancestor with chloroplasts but are not their immediate progenitors (see endosymbiont theory).