Tiny Clam-like thing? What is this hitchhiker?

[Brit’s Fish]

I just noticed this little guy on my rocks today… he’s anchored himself to a piece of live rock that had some different zoas on it. It has frilly edges like the edges of a clam shell but does not seem to react to shadows like a clam would. It’s fairly clear with the sides being more opaque & it definitely has a syphon-like mouth which is hard to see right now because it’s also fairly clear. I tried to capture the best pics I could but it’s in a harder place to get good front-on pics of.
What do you guys think? Some sort of anemone or tunicate?

 

[flabydab123]

Definitely a tunicate.

 

[Brit’s Fish]

Definitely a tunicate.

Sweet! I have some other hitchhiker tunicates on a wild rainbow lobo but they’re totally different looking. Same behavior though. They look like this (Google image).