? What is this?

[Frogger]

I believe manjano only get to be about an inch or so in size.

If it is a manjano they are considered very bad pests as they spread very quickly in the tank. I do not know if they move around, however you may have more than one of them which would explain in multiple places in your tank.

I would keep a close eye on it especially if you do not have any bubble tip anemones in your tank so therefore no reason to have a small one.

It is definitely not an Aiptasia