ID this thing on live rock?

[Donna421]

Earlier today while just gazing at the aquarium, we saw this thing move - opening and closing just a little bit like an oyster or clam. I'm fascinated by it and caught it closing (and maybe opening back up a little but not sure) in this video.

Any thoughts on what it could be?

If this info is helpful: We've had the tank running and this live rock in for about a month. We were told that the live rock came from the Gulf of Mexico off Florida (where we live), 13 miles offshore.

Link to video in my Google Photos.

Shared album from D 📸

Tap to view!

photos.app.goo.gl

 

[Reefer Reboot]

Looks like an oyster to me.

 

[alpha199]

Clam or oyster.