Can someone tell me what this is?
 

I cant seem to take any good photos of it. I did manage to take a short video on my phone.
i have two of them.
http://www.youtube.com/watch?v=M5AIW...ZhHXWjP7Ru_GFc

It has a tube like shell and uses a web like fishing net to eat. Kinda looks like a slug inside a tube. It is fun to watch. i feed them really big pieces of food sometimes just to watch them struggle with it.

Looks like a vermetid snail. Some say they are harmless, I say get rid of them before they start to multiply and become a problem. They can be a real nuisance.

I *think* it looks like a vermitid snail.. But I'm not too sure.

I'd say vermited as well. They are harmless from what I have heard. But can multiply and make an unsightly mess in your tank. This thread talks about it a bit and a few people give methods of removing them http://www.canreef.com/vbulletin/showthread.php?t=81093

Vermeti snail. They let out a web to catch food particles and reel them back in. I would try and get rid of the ones you see as they multiply fast like others have said. I had them in my nano tank. I got rid of a few by puttying or super glueing there "pipe/shell" shut. I tried to pry them off the rock but they just went deeper into their shell and were impossible to get out.

Good luck!