Bryozoan... or what? ID help

[Lotus99]

I have some kind of invert growing on some macroalga in my sump. It looks like white roots (the white stuff in the picture), but it's strongly attached, and this macroalgae doesn't grow roots. On another part of the same macro, I have a scypha sponge growing.

Any ideas? I'm just really curious. I hope it's not harmful in any way.