My first thought was Codium, but it's not the very familiar kind. So I did a quick search. There are 50 different species of Codium. I think what you have there is Codium cf. decorticatum.
Codium seems to be more "gumby" looking, more solid. This stuff seems to be cylindrical but you can kinda see through it. It's in the ballpark though. Lfs said halimeda family but I'm not buying that
I just can't find a picture/description that matches it