HELP what is this strange bug/creature?

[apexi]

I have had a new button polyp in my 180g for a couple weeks which has been doing great until just yesterday. Now it seems that the top section of the colony isn't opening up fully. Tonight I found 3 of these critters hiding in the polyps and was wondering if anybody knows what these are, and if they are harmful?





Here is a closeup of the polyps that aren't opening fully. You can see some kind of stub like extension protruding from the center. Anybody know what this is?? The rest of the polyps are closed tight, however even with the lights off and even if I touch these half open polyps with my gloves, they don't respond at all or close up. Are these polyps dead??