Zoa rock with clam/scallop?

[Smithhansen]

A couple weeks ago I bought this zoa from from my lfs and didn’t really think much about the rock it was on but I’m feeding my fish today and I see it move. I think it’s a scallop but I’m not sure

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[jcook54]

If it closes up, it's some sort of live clam/scallop. Very cool! I had a piece of live rock once that had the same thing but I ended up killing it because I didn't notice it when I removed the rock from my system. They're harmless filter feeders and a cool addition! I've got a few random clam-type things in one of my tanks too.