Can't ID this worm-like creature

About a week ago, I found a small creature on hidden in a creavice in my rock. Looked kind of like an tiny anemone. The "tentacles", or worms or whatever they are, they move independently and react to their surroundings but remain together at their base. Their color is yellow with thin black stripes.

Yesterday I found a second, separate, creature (same species) about a few inches away.

Being a newbie in this hobby, you could imagine my excitement at the site of the first creature. But now I see a second one in so little time and I fear for my tank.

I appologize to bring this to you guys so vaguely, but I the creatures are located in a very hard to reach place. Taking a clear pic of them is really hard. I will provide one as soon as possible.

Thank you all for your help. You guys have yet to let me down.

 

I'm fairly certain you have a spaghetti worm or sand mason worm.

They come in different colors and sizes. Basically, you will never see the worm itself as it will remain buried. You will only occassionally see the tentacles.
I couldn't find a good pic for you but here's one. If that is what you have, they are a good thing. http://depts.washington.edu/fhl/zoo432/falsebay/fbspecies/fbspecies.htm

I have actually purchased these on purpose from http://www.ipsf.com and http://www.inlandaquatics.com

You will see their populations rise and fall with the amount of excess food available for them.

 

Here's another interesting article of spaghetti worms from Hawaii's reefs. (Like I said, there are a number of varieties, colors, and sizes).

http://starbulletin.com/98/01/22/news/oceanwatch.html