Is it just those tentacles sticking out of a hole? I have some like that, and if they are near the sand they will make a tiny sand fort around there hole. If you watch, you'll see particles of sand or dietrus being drawn in along one tentacle into the hole, then pop out and be drawn out too the end of the other tentacle and let go.
Really no idea what it is, but wondered if yours was the same as mine. Mine have never left thier holes, and since one is right in the middle of a sps that actually grows too cover its fort I dont think they are doing any harm.
Good Luck