Yes...and no. It looks like some form of ulva, which is nice up until it's really not. It could be worse, though: I found a majano stuck to the shell of one of my snails the other day. Pretty!
Awww... He's just carrying a snack in case he runs out of algae in the tank. LolAhh, just did some research on Ulva, Man why does it have to be invasive, looks so cool. I guess Ill be treating him with some Hydrogen Peroxide tomorrow.
haha a majano on the shell, thats crazy.