All the lights are out in my tank and this little guy, about the size of a pencil eraser, jut started walking across the glass. Is this a nudibranch? Do I need to get him out of my tank? Let me know fast before he makes it to the other side!

Thanks

yes. add any zoanthids lately?

No, I have one small group of zoas that were the first coral I got for the tank over one month ago. The only new thing that I got recently were some pink xenias.

If you see one you have 10 or more, maybe the zoa eating variety may eat algae, who knows they usually eat one specific thing until there is no more and then they die.

Get rid of it....

Normally, you should get a specific ID, but nudibranchs are specialist feeders that are best kept out of the tank. They are often found with the corals they eat. Don't forget to check for eggs on your frag.