Parasite Got Your Tongue?
The female Cymothoa exigua will latch onto a fish's tongue, then extract blood until the tongue atrophies and falls off. By securing itself to the stub where the tongue used to be, the parasite become a stand-in tongue for the fish. The much-smaller males live in the fish's gill chamber, and may become female if there isn't already one in the fish's mouth.
from NOVA PBS
Key Facts In This Video
Adult Cymothoa exigua males can become females. (0:36)
A female Cymothoa exigua attaches herself to the base of a fish's tongue, then extracts blood from it until the tongue withers and dies. (1:02)
Male Cymothoa exigua living in a fish's gill chamber might mate with the female living in the mouth. (1:34)