Bony tongues in widest sense.
All members of the Osteoglossomorpha or bony tongued fish have several primitive features in common as there are upper and lower ribs, a peculiar kind of tongue, and usually a peculiar histology of the retina. The outer segments of the visual cells, both rods and cones, lie in bundles instead one by one in the tapetum nigrum. The lens also shows a peculiarity, most probably due to its chemical nature: in preserved specimens it remains transparent, in contrast to any other kind of fishes where the lens gets white, no matter whether treated with alcohol, formaldehyde or other kind of fixation. The Osteoglossomorpha have a particular kind of cycloid Scales , with a network of narrow sulci on the surface. All in all there exist some 25.000 species of fish—mainly of the bony kind.
The Osteoglossomorpha are the most primitive Teleostei, together with the Elopocephala, which in turn are subdivided into the Elopomorpha and Clupeocephala. This basis group of Teleostei is placed against the Euteleostei which comprise the vast majority of the orders and families of the bony fishes. It is, however, good to keep in mind that the composition and arrangement of the fish taxa higher than families is all but agreed by all ichthyologists.
The superorder is characterised by internal anatomical features, not easily seen on live specimens. Main characters are, according to Greenwood et al., 1966, verified by Li and Wilson, 1996:
»Primary bite between parasphenoid and tongue and paired tendon bones on the second hypobranchial or second hypobranchial and basibranchial«. All extant taxa of the superorder share another character, first described by Nelson, 1972, Li and Wilson, 1996, i.e. »the intestine passes to the left of the stomach.« Li and Wilson found four more characters unique to osteoglossomorphs:
a) There is only one epural, a bone dorsal to the urostyle supporting one or more caudal fin-rays (Tail skeleton ). The epural is without any connection to a vertebra or to the urostyle. In notopterids the epural is absent.
b) All osteoglossomorphs, except for the extinct lycopterids, do not have a supramaxilla, a bony or cartilaginous bar between maxilla and preethmoid.
c) There is no supraorbital, a dermal bone of the circumorbital series, found in all other teleosts.
d) Of this series of dermal bones around the orbit, in osteoglossomorphs the infraorbitals 4 and 5 are fused, except for the extinct Laeliichthys and Lycoptera.
The various taxa of the Osteoglossomorpha occur in the Americas, Africa, North and East Australia, South and Southeast Asia from India to some of the Indonesian islands, but not in other regions of Asia, except for the assumed stem-group Lycopteridae with Lycoptera, which occurred from the late Jurassic to early Cretaceous in East Asia between 30° N to 65°N. Another fossil genus, Thaumaturus (late Cretaceous to Palaeocene) has been described from Europe. All are freshwater fishes.
The Osteoglossomorpha comprise the order Hiodontiformes with the single family Hiodontidae and the order Osteoglossiformes.