I had the great pleasure yesterday of walking Rudy Raff back to his office after he gave a lecture on evolution to an auditorium full of undergraduates. Somehow we got to talking about this monster:
Let me introduce you to Cymothoa exigua, otherwise known as the Tongue-Eater or sometimes as the Tongue-eating louse. This little guy enters the gills of a fish and begins comsuming that poor fish’s tongue (its predator phase). When the tongue has either been wholly consumed or necrotic the tongue-eater attaches itself to the now-empty base where the tongue used to be. Helpfully (!!!), that tongue-eater then allows itself to be used as a new tongue for its host (the parasite phase).
This species takes control of its host’s organ, consumes it, and then functionally replaces that organ for the duration of its life! Like I said, it is both a predator and a parasite, so once it’s attached and performing tongue-y activities, the tongue-eater and the host live happily ever after.
If I had more time I’d mention environmental specialization and niche exploitation, but I’m sure you’re already thinking along those lines…