What is this cool little guy?

[Msmerek]

Ok so I've had this piece of live rock in my tank for about 7 months now and about a month ago I noticed this thing moves. More like opens and closes like a clam but it opens on the side that's against the rock. Anyone have a clue? It's right in the middle and looks like a curled tongue or something. Idk

 

[AcroNem]

It is indeed some kind of bivalve, not quite sure on species though.

 

[Msmerek]

Ya I kind of figured. He's a cool little guy though he will be open and then he gets startled and slams shut when something gets too close. Blew my mind the first time I noticed it. I just saw something move quickly on the rock and could not for the life of me figure out where the movement came from. Lol