Eating Through Stalk?
 

I just bought this 2-polyp frag on 9/23. It looks like something is eating through the stalk of one of the polyps. Has anyone seen this before? Anyone know what's happening?

I've never seen anything in that area eating it and, so far, it doesn't seem to be effecting the polyp itself because it's still opening fully. But this is obviously disconcerting. Any ideas?

Here is a progression over the past few days: 9/25, 9/28 and 9/29.

Wow, can't say I have seen anything like that before. All pics of pests I have seen typically start at the polyp skirt, which causes the polyp to completely retract.

Any updates? Is it worsening?

Sounds like zoa spider - a particularly nasty pest that burrows into the stalk of the zoa and eats it from the inside. Difficult to eradicate once you've got them. I'd suggest you get rid of the frag and check any other zoas you have. Do a search for more info as to how others have dealt with them. I found the only way was to inspect manually and it took several months, although I did have a lot of zoas.