Mitochondria, in reality mere subcellular organelles, were once dreamed by Scrooge McDuck to be a microscopic sapient species in their own right.
In a dream Scrooge McDuck experienced in 1983, he and his nephews used a Shrinking Machine to explore the cells of an oak tree leaf — where they discovered a fully-fledged civilisation of sentient Chloroplasts. In that dream-world, he was introduced to the Mitochondria as sentient firefly-like beings who lit up the “skies” of the cell at night; a few diligent ones could also be seen to fly about in the daytime.
Behind the scenes
The Mitochondria first appeared in the 1983 comic story Plantastic Voyage.