Brownish flat circle in display. Looks like an algae?

[Miami Reef]

These little brown flat circles get dislodged from my rocks sometimes. I believe I got these ever since I added KP live rock (Florida keys).

It doesn’t bother me, I’m just curious. What is this?

 

[Miami Reef]

Edit. I looked online and it seems to be a foot of a dead snail.

The ones that fall and can’t get back up and just end up dying.

 

[Miami Reef]

And coincidentally I added a lot of snails roughly around the same time as I added the KP rocks. So that makes sense.

 

[WheatToast]

Edit. I looked online and it seems to be a foot of a dead snail.

The ones that fall and can’t get back up and just end up dying.

+1
These are called opercula: