Heterotididae
Pantopontidae (butterflyfishes)
Singidididae (extinct)
Osteoglossidae (arowana)
Ostariostomidae (extinct)
Notopteridae (featherfin knifes)
Gymnarchidae
Mormyridae (elephantfishes)
Osteoglossiformes (Lat. "bony tongues") is a relatively primitve order of ray-finned fish.
Members of the order are notable for having toothed or bony tongues, and for having the forward part of the gastrointestinal tract pass to the left of the oesophagus and stomach (for all other fish it passes to the right).
One species, the arapaima (Arapaima gigas) is the largest freshwater fish known, with specimens reported up to 4.5 m in length.
The mooneyes (Hiodontidae) are often classified here, but may also be placed in a separate order Hiodontiformes.
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