Yep its like a plant and no reaction when touched..I took the picture to my local reef store here in Kansas City and no one knows what it is but they say its cool too..I bought 3 sepread rocks about 3 years ago and these things started 4 months ago.
Ya think I have something rare.
It looks plant-like because it is a plant. There are several families of red algae that have these very soft, inflated species. Without knowing which ocean it came out of & the time to go through my reference books I can't be more specific, sorry.