Cymothoa exigua

Cymothoa exigua, or the tongue-eating louse, is a parasitic isopod of the family Cymothoidae. It enters fish through the gills. The female attaches to the tongue, while the male attaches to the gill arches beneath and behind the female. Females are 8–29 mm (0.3–1.1 in) long and 4–14 mm (0.16–0.55 in) wide. Males are about 7.5–15 mm (0.3–0.6 in) long and 3–7 mm (0.12–0.28 in) wide. The parasite severs the blood vessels in the fish's tongue, causing the tongue to fall off. It then attaches itself to the remaining stub of tongue and the parasite itself effectively serves as the fish's new "tongue".