This Parasite Eats a Fish’s Tongue — And Takes Its Place
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in the Gulf of California there actually exists a critter, Cymothoa exigua, that targets a fish by infiltrating its gills and latching onto its tongue. It proceeds to not only consume the organ, but will then replace it with its own body, providing the fish with a new fully functioning tongue it uses (probably a bit begrudgingly) to grind food against tiny teeth on the roof of its mouth.

This remarkable attack is the only known instance in the animal kingdom of a parasite functionally replacing an organ of its host. And while C. exigua targets several other fish, attaching to their tongues and draining their blood, only with the rose snapper does it devour and completely replace the organ as an operating structure, according to marine biologist Rick Brusca of the University of Arizona. And he stresses that while there are hundreds of such species of tongue-targeting isopods, contrary to many media reports, only C. exigua can actually truly assume the duties of the organ.