Invert hitchiker ID

[Palmer]

I noticed this hitchhiker about a month ago. It is hard to see it in the picture since it's whole body is a clear sac except for the 4 or 5 antenna/tubes/sticks that come out of it. I have looked through a number of sources and the only thing that seems to come close to this is some sort of sea pen but I am not sure never having seen one up close. I have seen it twice once at the base of my live rock attached to it with antenna upward and today under an arch in my live rock with antenna going forward towards the open water.

Any thoughts on what this is?

[IMG][/IMG]