Well, if it is mold, then your up that famous creek, so sample it, if it taste good then it is worth bottling. If you do rack without disturbing it and leave the surface layer intack and discard.
Be warned strange things growing in your beer can suddenly take your beer down a few points and make lots of CO2 which would be bad, other yeasts and microbes can eat the high order sugar that beer yeast does not. Anything suspect like that I put the bottles in a plastic bin, so if they go for a high order kinda finish the SWMBO does not demand and end to beer brewing!
My opinion it is a mold