slug

What is this???? About the size of a nickel Disappeared when I turned lights on.

Found this guy, haven't added anything new to the tank in over a month and he just appeared. Seems to be cleaning and minding his own business. He looks like a snail with no shell. (I think we call those slugs? Lol ) I am not putting corals or anything in here so is he safe to stay or should I...

Plz I have a reef aquarium and would like to know if there is any coral/anemone safe sea slugs which are visually appealing and only eat algae/uneaten food.

Hi guys, I just noticed this little creature appeared in my tank! It's probably a hitchiker ( i didn't add anything in my tank for over 2 months though?) but anyways. I would like to know what is it? I think it looks like a sea slug? Or a snail? I have no idea so i'm uploading this video and...