So they're fully adapted to the undersea environment... I always thought they might have to be, in some manner. [It's indeed very cool to Mulder, and it's really just for his own interest that he wants to know.] There must be so much culture, so much knowledge that could be found by interacting with them. I have to wonder why they've kept themselves so separate from us, all of this time... but then again, knowing the ways of people on the surface, I almost can't blame them.