Yup that's exactly itI've had them both before and they don't really spread and don't harm anything.
Is this the worm in the top video?
http://www.melevsreef.com/critters/spionid-worm
I had so many stomatella snails before to the point where I was giving them away for free. @RavenSF I wish I had known you earlier, I woulda given you some as well. Anyways like raven says, super harmless. Also super ugly imo.
Population went away after I introduced a either a coris wrasse or cleaner shimp. Forgot which, but I'm pretty sure either of them had something to do with it..