I myself must admit that I was very very nervous when multiple people told me my green gig was a haddoni... I had the luxury of standing at the LFS and watching the anemones posture, which screamed Gig to me.. I was able to see some purple verracue there, so when I brought it home, my lame picture taking showed none, and it didn't worry me as much. Now that he's turning into a shag rag, it confirms the research I did on the back end.
Are you able to physically get to this animal? That would be the most helpful thing, as well as knowing what to look for. The one thing I will say is, when I went in to look at my Gig, there were two green haddonis two feet away so I was a clear example of green haddoni vs green gig. One observation is the haddonis had a mouth area that looked just like the one pictured here in this thing. There was much more yellow in the ring, and the ring around the mouth was much larger.. On the contrary, if you look at my green gig, there is no yellow even around his mouth (I've only seen yellow ring around the mouth a couple of times)..
Pictures of the underside of my gig that everyone was doubting was a gig.
Even when our gig looked like a haddoni a bit and was all tightened up, his mouth was always tight, and never had any yellow.
Even now when the current flips our gigs pedal around, I don't really see much verracue on the underside. I've seen other people's green gigs still have a colored column, and ours has a very bland color as you can see unlike our purple which is very blue.
In the end, I dont know, but I"m sticking with haddoni based on the mouth, the posture, and seeing little on the underside, but I might be wrong. If you can get to the animal and get a good look at'em, you just might have a green gig on your hands. Maybe these gigs (with little verracue, no foot color, haddoni looking) are coming from a certain part of the world that is different than others. I don't know, but good luck and keep us posted.
Take a look at 9 o'clock and you will see faint blue lines that appear to be veracue. Typically Haddoni's also have that ring around the rim giving the appearance of thicker more densely packed tentacles on the edge. I didn't see that in one of the earlier pics above.
If you take a look at xtlosx's thread many (including myself) doubted his gig was truly a gig.
I'll admit I very well could be mistaken, but based upon what has been shown, I believe it is a gigantea.