The Cymothoidae are a family of isopods in the suborder Cymothoida and are found in both marine and freshwater environments. Cymoithoids are ectoparasites, usually of fish, and among their number they include the bizarre "tongue-biter" (Cymothoa exigua) which attaches to a fish's tongue causing it to atrophy, and replaces the tongue with its own body. Around 40 genera and more than 380 species of cymothoid are recognised.