...from the first version I swore to myself I was looking at a shackle connected to something...
I have not previously joined in the "imagineering" associated with the underwater photos, and have generally been unable to see, with any degree of confidence, what others have been pointing out. However, honesty compels me to admit that
the one thing to date (aside from the obvious wire, etc. from previous missions) that I think might be man-made is what you identify as a shackle, I also perceive it as possibly being that. I believe Jeff Glickman suggested it was a "pulley" last night, but the commentary ran by awfully fast.
I am, so far, neutral about the delta anchor. For some reason I am unable to get your link to the anchor to work, but there are plenty of other anchor pictures out there.