Weird snail thingy thing..need id

[eleer]

This thing that looks like a snail which looks like it has antennas but i dont know what it is. It lives inside a tube which came with my hammer coral frag. It excretes a long white thread film or slime. I think it acts as a net to catch food because i was watching it and it pulls the white slime back in whenever it catches anything. I also know my peppermint shrimp really wants to eat it, but it goes back down in its tube too fast. Here's the best pic i can get of the thing.....

 

Thanks for your help

 

[Graywolf57]

I think it may be one of these:

 

http://www.globaldialog.com/~jrice/invert_...ge/vermetid.htm