Does any one know what this is

[big man]

I looked on my hammer coral and something was growing on it. It doesn't look like a feather duster. And if I observe it for a little bit it looks like it has a mouth that's moving

 

[MoshJosh]

vermetid snail. I would use tweezer to "gently" crush the base. Crushing just the upper most tube will not kill it.

 

[slopigyo]

Crush it outside the tank and wipe it clean with a toothbrush before you put it back in if you go that route

 

[big man]

Thanks