I saw this in my main tank this evening. I noticed the tentacles moving and it didn't stand out as a living being since it was white colored. But then I watched it move from the live rock ACROSS a gap to the astrea snail sitting to the left! I had my camera in hand and got some pictures of it. The last shot is probably the best.

I am thinking it is some type of Nudibranch or a snail without its shell, but I really don't know. I want to identify it so I can determine if it needs to be removed or not. Thanks!

It is a Stomatella varia, a common hitch hiker and beneficial algae grazer. They tend to be nocturnal but you sometimes see them when the lights are on.

i have those all over my tanks

I had a ton in my nano, until I added my mantis :)

Yep, they're beneficial for sure. I can hardly flip a rock in my 120 without seeing one.

Cool, thanks Carmie and everyone else. Sounds like its a good thing to have around. This was the first time I have seen it in my tank, so I had no idea what it was. Thanks! :)