Identification of white slug (pictures included)

[Tg822]

Hello all, need some help identifying this little hitchhiker. I've been cycling my bio cube 29 for about 5 days and this morning I noticed him on the glass. I've already had to deal with getting rid of aiptasia so I hope he comes in peace.

 

[jeperry3]

It's going to be hard to ID with those pictures. Does it have a sort of shell? If so could be stomatella snail, which is good.

Is it free swimming as appears in one picture. Could be a nudibranch. Many are coral predators. Better pics needed for a positive ID.