Chimaeras are cartilaginous fish in the order Chimaeriformes, known informally as ghost sharks, ratfish (not to be confused with the rattails), spookfish (not to be confused with the true spookfish of the family Opisthoproctidae), or rabbitfishes (not to be confused with the true rabbitfishes of the family Siganidae). They may be the “oldest and most enigmatic groups of fishes alive today”.