Cannoli with green filling

[blackdog]

This interesting critter came with my SFW crew package today. It was labeled "Replacement for cucumber"

Is this a sea squirt? I remember seeing a photo somewhere, but now I can't locate one. Can anyone point me toward info about care for them?
I'm very curious to see where and what shape it will be in the morning. It hasn't changed location since I dropped it in around noon, but it has shifted around. I spent extra time acclimating it, thinking it might be sensitive like a star or something.

 

[ebeckels]

guess: maybe a nudibranch?

 

[blackdog]

I'm going to bump this message, just because it doesn't look like many people saw it. I'm having trouble figuring out whether this is a cucumber or a tunicate or what the heck it is. It doesn't really resemble anything I've been able to find online.
It hasn't changed location at all still, but frequently morphs one or both ends to be more open or closed to the current. It is symmetrical in that both ends look the same. You can see there is some type of mouth or anus or both at the center of the green filling.
It has not done anything that resembles sifting the sand. At night it closed up both ends and appeared to "sleep."
I'll e-mail SWF on Monday, since they're the ones who sent it to me. I'm happy with my package, but labeling an animal "substution for cucumber" makes it very difficult for me to determine proper care.

 

[blackdog]

I heard back from SWF about my cannoli (same day--very impressive).
Turns out it is a pair of umbrella mushrooms, which they were substituting for cukes last week.
Now that it has been a few days, they spend more of their time spread open, which makes them look more mushroom-like and less nudibranch-like.
They are very nice, and have a nice green glow. However, they don't do much for stirring my sand, which was my goal. Plus I didn't consider my tank ready for corals. I'm hoping my parameters will continue to be stable. We'll see how everything reacts to a dying feather duster. One of the ones from my shipment ejected his feathers, then left his tube, and is now dying on the sand.
All in all, I guess I'm glad SWF didn't postpone shipping my order until they had cucumbers. And I imagine I got a good value getting mushrooms instead of cukes.