Purist, schmurist, here's my take: the warrior aliens in Cameron's film all had nude heads; that is, the translucent sheath that covered the distinctive skull of the creature in the first movie was absent. The queen, however, had a translucent sheath that was downright hypertrophic. My theory is that the first alien out of the eggs--one that, like the creature in the first film, has a sheath--will eventually metamorphose into a queen and set up a colony. Indeed, that was probably what the alien was doing when it was hidden on the Nostromo's shuttle, the Narcissus: preparing for its final metamorphosis.
But, um, that's only when I'm not being a purist.