well, not completely wrong but still wrong! Osteoglossiformes is an Order not family, all arowanas and arapaima are in the same family Osteoglossidae; knifes,mormyrids are in the same Order with arowana and pima but in a different suborder, knifes and mormyrids are in two different family!
*order Osteoglossiformes
-suborder Notopteroidei
family Gymnarchidae (abas)
family Mormyridae (elephantfishes)
family Notopteridae (featherback knives)
-Suborder Osteoglossoidei
family Osteoglossidae (arowanas, arapima)
family Pantodontidae (butterflyfishes)