Fig. 26.13 Chlorarachnion with its quadruple membraned chloroplasts and Euglena with triple
membraned chloroplasts. Chlorarachnion are amoeboid algae which have chloroplasts that are
surrounded by four membranes. A two membrane structure is customary for chloroplasts. This
unique four membrane structure suggests that the chloroplasts in Chlorarachnion were acquired by
ingestion of a eukaryotic algae. Thus, it is believed that the chloroplasts in Chlorarachnion were
created by a two stage process. An ancestral, double membraned, chloroplast would have been
created by primary symbiosis when some unknown eukaryote ingested a photosynthetic bacterium.
After that eukaryote was in turn ingested by yet another eukaryote, through secondary symbiosis the
plastid would have been retained in a form that was surrounded by the quadruple membrane. The
upper image is titled “Chlorarachnion reptans.jpg” by author ja:User:NEON/commons:User:
NEON_ja and it is being used under a Creative Commons Attribution-Share Alike 2.5 Generic
license. Euglena have chloroplasts that are bounded by three membranes, as do some
26 The Game of Evolution Is Won by Competitive Cheating
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