Dirty Clean-Up Crew--what's this?

[JoJosReef]

I'm thinking this is a type of turf algae. So far it is only growing on the shells of two Astraeas. Both Astraeas coincidentally have the same stalk macro growing, too, which I am assuming is a type of Acetabularia macro, but not certain. The turf definitely has a mossy feel and texture to it. I cleaned off both snails, but I'm sure it'll come back at some point. Thoughts?

 

[JoJosReef]

P.s., it is only on the two snail shells, not on any of the rocks or other surfaces in the tank.

 

[aztoza]

Weird!