Are any bacteria visible to the naked eye?
Viruses, Bacteria, Protists, and Fungi
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Epulopiscium fishelsoni, which lives in the gut of the brown surgeonfish (Acanthurus nigrofuscus), is visible to naked eye. It was first identified in 1985 and mistakenly classified as a protozoan. Later studies analyzed the organism’s genetic material and proved it to be a bacterium of unprecedented size: 0.015 inches (0.38 millimeters) in diameter, or about the size of a period in a small-print book.