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). However, this similarity is thought to have evolved independently of plant chloroplasts. 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.