Osteoglossomorph

arawana

osteoglossomorph, (superorder Osteoglossomorpha), any member of what is widely believed to be the most primitive group of bony fishes. This reputation stems from their rudimentary caudal skeleton and the lack of a set of intermuscular bones throughout the abdominal and anterior caudal regions of the body. Osteoglossomorphs are unique among fishes in that they use their tongue as the opposing surface for the teeth when they bite into food. They are divided into two orders, Osteoglossiformes and Hiodontiformes. Osteoglossiforms are a group of morphologically and biologically diverse forms primarily found in freshwater environments in Africa, Asia, South America, Australia, and islands of the tropical Pacific Ocean; however, a few osteoglossiform species enter slightly brackish water. In contrast, hiodontiforms occur only in North America and are probably the most primitive group of living osteoglossomorphs.