I call this my weed because the original has spread to every surrounding rock and is just huge. I would like to know what it is. The first picture is when it is "open". The second is when it is "dormant"
The first picture looks to me like a s[ecies of hydroid. Not fun . . . . trust me.
Some limpets will actually eat them from what I have heard, but the kind that I had must not have tasted good or something. They continue to grow and I actually have sessile jellyfish now.