Cymothoa is a parasite that burrows into the tongue of certain fish species. There, it begins to suck the blood supply that nourishes the tongue, causing it to lose its blood flow, atrophy, and eventually fall off. When this happens, the parasite takes over, controlling the tongue muscles and replacing it to feed on what the fish ingests.
All these parasites are born male; but when they manage to colonize the mouth of a fish, they transform into a female; this is the sex they will maintain throughout their adult life. When one of these parasites reaches a mouth that has already been colonized, it will no longer be able to develop female reproductive organs; therefore, it will simply reproduce with the male it finds in the fish’s mouth.
Very little is actually known about this animal; but there are no known cases of this parasitic animal affecting humans.
