I have a lot of hitchhiker feather dusters (dime to nickel sized) that my coral beauty doesn't touch, but I don't have cocoworms in particular.
I see him picking at the rock all day, he may or may not be eating sponge. Most of the sponges in my tank live under and between the rocks where they aren't reachable so I don't know if that means that he gets the reachable ones before they get big or they just don't grow in those areas *shrug*
Dunno if that helps but that's my experience!!
