MAD SNAIL!

I'v got a snail like that with a big hunk of coralline on it also. Now some sponges have decided to propogate on the branches of the coraline.

... the plants on the backs are pinkish-white and they look like a strain of calerpa, but I'm still trying to I.D. them. I'll let you know.

phylum rotophyta looks like correa(boxs that make a chain) or bosslia(little hearts stacked on top of each other)

Thank you socalreefer...but they have a single stock with leaves? coming off of it.. looks a little like evergreen leaves....weird.