I need help identifying!!!! please help!


Reefing newb
I am fairly new to the saltwater aquarium hobby, I just recently did a water change and noticed this white sack on my live rock. I have a clownfish and a hermit crab along with five or so snails. I also have a wide rage of soft corals. Anyway the sack is oddly shaped and when I pulled it out of the water it smelled very rancid. I cleaned it off and now a few days later i am seeing another one! I really would like help to find out what this is! thanks! :frustrat:

I added the best photo i could take. i poked it and it popped so thats why it isnt really a sack anymore.