I always thought of it more like their tongue, since it doesn't appear to have a throat-hole. That, and the fact that Ridley Scott intended the Xenomorph to have that kind of violently rapey nature, you know, like "I'm gonna violate you with my tongue...that happens to be another set of teeth!" But I agree, the head of a Sheegoth does have a striking similarity to that of a Xeno. On a more relevant note, (my apologies to the artist for steering the conversation elsewhere), I always loved these creatures two reasons: 1) The aforementioned Xenomorph resemblance gives them an intimidating and badass look; and 2) Their main weakness is my favorite weapon in the game, to the point where I absolutely despise anything that isn't affected by it, thus forcing me to switch to something else! I am of course talking about the almighty Plasma Beam!