I recall a letter in the back of a 90s Namor comic where someone said he should be called Marvel's first hybrid, and the response was that the little wings on his feet are what make him a mutant.

Of course there's a whole subsection on the topic in his Wikipedia entry: en.wikipedia.org/wiki/Namor#%... "He has principal characteristics that neither Atlanteans... nor humans... possess. These include his ability to fly, and possibly his durability and strength."

Namor - Wikipedia