I've got a bunch of different sponges on my rocks, and most of them seem to be doing ok, but there's a couple that look...weird. The majority of them are smooth, but these look different. Are they even sponges? Some kind of coral? An egg sack of some kind? I don't know, but I'd like to learn. Pictures below.
I've never heard of that happening, but maybe others can chime in on that.

