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Which eukaryotic organism is known to lack mitochondria?

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Fluorescent confocal image of HeLa cells with green microtubules outlining cell shapes, red mitochondria, and blue nuclei. — mitochondrion Mitochondria (red) are found throughout the cytoplasm of almost all eukaryotic cells (cell nucleus is shown in blue; cytoskeleton is shown in yellow).

The only eukaryotic organism known to lack mitochondria is the oxymonad Monocercomonoides species.12

While most eukaryotic cells rely on mitochondria for energy production, Monocercomonoides has adapted to function without them, utilizing alternative metabolic pathways to meet its energy needs. It is important to distinguish this from organisms that possess hydrogenosomes, which are specialized, membrane-bound organelles that serve as energy-producing substitutes for mitochondria in certain anaerobic eukaryotes.123