Id this worm?...or....hmm well i dont know what to call it.

[parkinsn]

It looks like a vermetid snail to me, kinda hard to tell from the pic. Is it a hard shell? (oops just read OP it is a hard shell) My guess still stands then.

http://www.wetwebmedia.com/MolluscPI...besnailidf.htm

[zum14]

awesome! thanks very much. Some good reads.

[Madreefer]

Over the years I've had 2 of them. Forgot what they are called, not harmful but I hated the web or strings as well. Just find the hard shell he lives in and break it apart and kill him.

[whatcaneyedo]

+2 for vermetid snail and just in case you wanted another article:

Snails That Worm Their Way Into Tanks
http://reefkeeping.com/issues/2005-01/rs/index.php