If there is any more stages after the adult alien, what could they be, they start of as egg, then facehugger, if host is human a snake like chestburster will emerge, it later changes into a humanoid like creature with some chestburster features still remaining, tail and long head.
I was wondering, if the alien changed again, would it look more human, something like Giger's Species designs, but without a face and only a mouth?
just a thought, what do you think?