- The Tetraodontiformes (/tɛtrə.ɒˈdɒntɪfɔːrmiːz/) are an order of highly derived ray-finned fish, also called the Plectognathi. Sometimes these are classified as a suborder of the order Perciformes. The Tetraodontiformes are represented by 10 extant families and at least 349 species overall; most are marine and dwell in and around tropical coral reefs, but a few species are found in freshwater streams and estuaries. They have no close relatives, and descend from a line of coral-dwelling species that emerged around 80 million years ago.