The bony-tongued fishes make up the order Osteoglossiformes. This order is a relatively primitive or basal order of ray-finned fishes. The group contains a wide variety of fishes from the giant arapaima of the amazon the tiny feather-fin knife-fishes and freshwater butterflyfish. The classification of the order comes from a few morphological similarities. In particular, most fish in this group have a kind of bony-tongue. Often this tongue has teeth on it and is used to crush down against the teeth on the top of the mouth.