The world's smallest animal is smaller than a human red blood cell
The microscopic parasite Myxobolus shekel measures only 8.5 micrometers, making this fully grown animal smaller than a human red blood cell and challenging the traditional biological definitions of multicellular complexity.
Myxobolus shekel represents the extreme limit of animal reduction, measuring a mere 8.5 micrometers in diameter. While most animals evolved toward greater complexity, this myxozoan parasite took the opposite path after diverging from cnidarian ancestors roughly 500 million years ago. By sacrificing nearly all typical animal features—including organs, nerves, and a traditional gut—it transitioned into a streamlined existence within the brains of fish.
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