|Location||Gulf of California south to north of the Gulf of Guayaquil, Ecuador. Two host records were also recently discovered in Costa Rica|
|Conservation Status||Not Evaluated|
|Scientific Name||Cymothoa exigua|
The Tongue-eating louse (Cymothoa exigua), is a parasitic crustacean of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself at the base of the fish's tongue. The female attaches to the tongue and the male attaches on the gill arches beneath and behind the female. Females are 8–29 millimetres (0.3–1.1 in) long and 4–14 mm (0.16–0.55 in) in maximum width. Males are approximately 7.5–15 mm (0.3–0.6 in) long and 3–7 mm (0.12–0.28 in) wide. The parasite destroys the fish's tongue, and then attaches itself to the stub of what was once its tongue and becomes the fish's new tongue.
Cymothoa exigua extracts blood through the claws on its front, causing the tongue to atrophy from lack of blood. The parasite then replaces the fish's tongue by attaching its own body to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue. It appears that the parasite does not cause any other damage to the host fish. Once C. exigua replaces the tongue, some feed on the host's blood and many others feed on fish mucus. This is the only known case of a parasite functionally replacing a host organ. There are many species of Cymothoa, but only C. exigua is known to consume and replace its host's tongue.