EDIT - FINAL DESIGN
So the task was to design the Bloodworm Helmet, I looked into something really organic. The original design is very heavy and built with a single piece, and i tried to have something with different parts, with for inspirations stuffs like the facehugger and some creepy insects.
I first did some shapes, trying closed and opens helmets

The most closed helmet gave this organic/invading look i was trying to get, so i rendered some.





I think you should keep in
I think you should keep in mind that the helmet its-self is made from troll bone, having the design akin to something more insect-like seems very pointless. What's the point of having it made from troll bone in the lore, if it is not clearly shown in the actual design? Remember that just because it's in morrowind does not mean it HAS to look completely alien/Foreign. I would suggest going for something perhaps slightly more Nordic, which would mirror the original very well, or perhaps something elvish (High elvish) as the creator of the helmet was mannimarco.