cool invert

This is a picture of an invert that just appeared on my green star polyps.  Anyone know what this is?  It feeds by extending a piece of sticky string like substance, and when ever food floats by like brineshrimp it will stick to it and the the little invert pulls the string in and eats whats attached to it.  It also has a hard tube that goes clear around my coral and a hard disk just like a snail has for defense, to cover up the end of the tube when it feels threatened.

From the pic, it looks like the back of a small shrimp or a pod, like pistonfister said. But from the description you gave, I think its just a tube worm of some sort. No worries...