Hard to tell in the picture. Looks like it may be a copepod. If so they are a good thing to have. That eat anything just about along with fish waste and most fish love to eat them. Harmless great tank addition. Did it look like this?
I don't know what it is but if u don't like it u can just remove it. Scrap or brush it off and vacuum or net it out. I recommend turning off power heads before u do because it will go everywhere. Good luck with the tank! First one?