Cymothoa exigua is a species of undersea louse that has adopted a peculiar way to survive. It targets the rose snapper fish and enters its body through the gills. From there, it attaches itself to the fish’s tongue and takes over. The louse cuts off the blood supply to the tongue and consumes the organ and then takes the tongue’s place.
It is the only known instance in the animal kingdom of a parasite functionally replacing an organ of its host. Although the louse targets several other fish, it is only with the rose snapper that it remains after feasting on the tongue.
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