Congo eel

Indeed, it is superficially so like a fish that it is known locally as the Congo eel.

Congo eel, amphibians of the genus Amphiuma (order Caudata)

Along the way we learn a variety of fascinating and often bizarre facts: the Congo eel salamander has more DNA per cell than any other vertebrate; female birds are XY in terms of chromosomes while female mammals are XX; and many more.