Found something interesting in Symbiotic Planet: A new view of evolution. It's well established that plastids and mitochondria in eukaryotes are prokaryotes assimilated into larger beings and turned into organelles through endosymbiosis. But the author here outlines symbiosis as the key mover in evolution and adds a third endosymbiotic organelle, centrioles/kinetosomes, which she claims derive from spirochetes and are the first merger to have taken place in biological history. She admits this is an extreme and fringe view with little evidence. This is the first time I hear of this. She also mentions that in earlier literature the nucleus itself was debated as the result of endosymbiosis but does not believe it because there are no extant nucleus-like prokaryotes.