Cymothoa exigua is a parasitic isopod that attacks fish. It enters in through the gills and attaches itself to 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.
Despite its repulsive appearance and lifestyle, Cymothoa exigua is harmless to humans though it can bite if someone attempts to pick it up.