Scientists studying a species of ray-finned fish made a startling discovery a parasite had replaced the tongue of its host.An X-ray image of a wrassess skull showed a small crustacean inside the mouth that has been feasting on liquid in the muscular organ.The small isopod, also called fish lice or tongue-eating louse, paralyzes the fishs tongue and sucks nutrients until it withers away.The parasite eventually replaces the organ, attaching in the location and leaving just the underlying bone.An X-ray image of a wrassess skull showed a small crustacean inside the mouth that has been feasting on liquid from the muscular organ untilThe isopod belongs to the genus Cymthoa and was discovered inside a fish pulled from Australian waters.Kory Evans, an assistant professor in the Department of BioSciences at Rice University in Houston, Texas, spotted the small creature while conducting a CT scan on a wrasses skull.Found a tongue-eating isopod (purple) in one of our wrasse scans this morning while digitizing it. These parasites attach themselves to the tongues of fishes and effectively become the new tongue...horrifying, Evans shared in a tweet regarding the discovery.Spotting one of these terrifying parasites is very rare, but experts know it attaches itself inside its hosts mouth and feeds on the tongue.The small isopod, also called fish lice or tongue-eating louse, paralyzes the fishs tongue and sucks nutrients until it withers awayIt first releases anti-coagulants to prevent the fishs blood from clotting and attaches to organ in order to extract blood and mucus from it.The tongue eventually withers away and the isopod replaces it acting as the fishs acting tongue.Though the isopod seems scary (in fact, it was the inspiration behind the 2012 horror film The Bay), little harm is done to the fish aside from the removal of its tongue, Evans shared in a blog post.The isopods body acts as a functional tongue, and feeds on mucus secreted by the fish. This is actually the only parasitic animal known to functionally replace one of its hosts organs.The tongue eventually withers away and the isopod replaces it acting as the fishs acting tongue. Pictured is an example of the parasite inside a fish's mouthThere are 380 different known species of tongue-eating isopods, most of which usually have a specific species of fish that they invade and feast upon.Although little is known about the lifecycle of these creatures, experts have found evidence that females may mate with male isopods living in the fishs gill chamber.Another underwater parasite dubbed vampire fish was spotted in a freshwater lake in Vermont, hundreds of miles away from its natural habitat in the Atlantic Ocean.The sea lampreys are described as a 'nuisance species' by the Vermont Fish & Wildlife, and survive by parasitizing other fish, attaching to their bodies and sucking out blood and other body fluids for sustenance.Another underwater parasite dubbed vampire fish was spotted in a freshwater lake in Vermont, hundreds of miles away from its natural habitat in the Atlantic Ocean The sea lampreys are described as a 'nuisance species' by the Vermont Fish & Wildlife, and survive by parasitizing other fish, attaching to their bodies and sucking out blood and other body fluids for sustenance State officials say they have contained the most threatening sea lamprey population in Lake Champlain near the Canadian border.The younger larval lampreys can spend as much as five years in a sedentary state, burrowed beneath the sandy river bottoms slowly filtering out small food particles form the water.Once they mature, the swim back downstream to the Atlantic Ocean, where they spend the bulk of their lives feeding off the blood of other fish.In the past sea lampreys have had a devastating impact on freshwater fish populations, with one capable of killing an average of 40 pounds of fish in a year.