In this week's Big Issue I found the following story:
A shocked insect specialist who was confronted with two black beady eyes in the mouth of the red snapper fish he was about to cook had come face to face with a tongue-eating ipsopod - the only parasite that eats and replaces an organ of its host. The Californian crustacean, found by Dr Jim Brock, enters a fish's gills, and when its host's tongue shrivels to a stub, the fully grown louse acts as a replacement tongue, with its head facing out of the mouth. It will now be exhibited at the Horniman Museum in south London.