The chloroplasts were presumably acquired by ingesting some green alga. They are surrounded by four membranes, the outermost of which is continuous with the endoplasmic reticulum, and contain a small nucleomorph between the middle two, which is a remnant of the alga's nucleus. This contains a small amount of DNA and divides without forming a mitotic spindle. The origin of the chloroplasts from green algae is supported by their pigmentation, which includes chlorophylls a and b, and by genetic similarities. The only other group of algae that contain nucleomorphs are the cryptomonads, but their chloroplasts seem to be derived from a red alga.
The chlorarachniophytes only include four genera: Chlorarachnion, Gymnochlora, Lotharella, and Cryptochlora. These show some variation in their life-cycles and may lack one or two of the stages described above. They have mitochondria with tubular cristae, and a few other such groups have been considered possible relatives, notably the cercomonads[?]. The euglenids have also been considered possible relatives, but this is based entirely on the presence of secondary green chloroplasts and is contradicted by structural and genetic studies.
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