Somewhere, Tintenfisch mentioned that she ran across numerous oddities as well as finding photos of some with branching arms but I could not find the discussion but here is one of (or one similar) the pictures of the branching anomoly
It is hard to tell about the mantle since the live photo is a post brood (or possibly prebrood with eggs) female and after formalin the animals look quite different than in real life. Cassy prebrood with eggs had a similar odd look to the mantle.
That was this thread. The octos had 8 'normal'-looking arms at the bases, but the tips split into many branches. In the instance above, here, it looks like a similar thing has happened but only once, and nearer the base of the arm, so that it looks like a whole extra arm.
Didn't we have a threat about a penta- or hexapus recently, too?
The last discussion I remember was when this one (in the original topic of the post) was first by the restaurant but I am batting 0 on finding things this week (but I DID find a reference to the post I was looking for and you found Kat )
Wow, the branching arms are cool. As someone said on that thread, my first thought was injury then regrowth issues, I've seen it in lizards like this one -
But that would need the octo to be losing arms almost constantly and the same fault happening each time, would she even survive so many injuries?
The thing I liked about the nine armed one is that it's all regular, humans with extra fingers or toes for example often have one that isn't quite right, but all the 9 arms seem perfectly normal, I'm not sure what that says, but it's just pretty cool.