ID please

[sn8kbyt]

Just noticed this little guy tonight. Whenever he senses movement he sucks himself completely into the rock. To the point that you cant even notice the little hole he popped out of.
I don't have a picture tonight but I have about 3-4 what I am gong to call "clams" for the lack of a better ID that came on the primo deco Florida live rock I bought. They are all covered in algae and what not but for describing purposes are basically 2 shells stuck to the rock, and look like clams. You can poke them and they move slightly but secured to the live it seems without using a lot of force. So here is the thing I have seen them move or jerk now twice when I shut off the filters and feed the fish. Is it possible they survived and are actually alive? If yes are they something that is of concern?

 

[bang guy]

It's a type of Bristle worm commonly called a Feather Duster or Fan Worm.
Your clam looking critter is probably a Turkey Wing Clam but I would require a much better description of a good picture for a positive ID.

 

[sn8kbyt]

Here is a picture of 3 of the clams in my tank I have at least 3 more that size but have only seen 2 of them move. Got this pic today and it was opened up a little and closed when I got home.

 

[jay0705]

I have like ten of those clams on my lr. Alive and well idk what there eating. Lol must be getting something out of the water

 

[bang guy]

Yep, Turkey Wing Clams.