We purchased live rock at a local store and we have a worm like friend that
came with it. I'm hoping someone can help me identify? It looks like a worm
about an inch long and 5-8mm in diameter.

I first noticed the hitch hiker a day after we put the rock into our tank. It
appears it comes out at night but doesn't receed right away. When it isn't
out it looks just like the rock, almost like a shell.

I have a picture in my photo gallary and will try to attach the picture to
this. I am new to this site and not quite sure how to navigate.