what is this?

[Angyf71]

Anyone know what this is? The small white things are all over my live rock and snail shells and the larger, darker thing has a little worm coming from the center http://instagram.com/p/mMSB5cNdjs/

[julie180]

Pictures?

[Angyf71]

http://instagram.com/p/mMSB5cNdjs/ sorry, for some reason I'm having trouble with pix. I hope this one works