Some sort of bivalve or something on my rock


Reefing newb
There are about 4 or 5 of these on part of a rock in my tank.
They look almost like a clam or oyster or something, and have green/yellow branches coming out of them. They also have what looks like a mouth that extends out, and looks like a funnel.

Here's a pic

Looked up turkey clam but no luck =\

They almost look like they're built INTO the rock, and you just see them open and close with their big funnel mouths poking out, and the bright green/yellow branch things. I'm turning that rock into a zoa rock and I just need to know what these are before hand