That stone is awesome, great work in tying it as it looks very realistic.
Around Thanksgiving, I was surfing the 'net on the Fly Tying Forum/Hatches Magazine and found an articulated black stonefly nymph that had been tied with black bead chain by Dean Myers. I though it was a cool idea to use bead chain because you can get the articulation without using mono to tie on the lower abdomen. In the water the tail should fish-tail back & forth to mimic a swimming nymph. It should also work for the helgi nymph. Here is the link:
I haven't tied the stonefly yet, but I intend to do so shortly. You could tie on additional goose biots to represent the legs, etc.
Just my $0.02.