slugs in my tank

[LoneStar45]

I am wondering about a couple of little creatures roaming in my tank. They are white looking slugs. They are too small to get a good picture, but they are definately some type of slug. If someone knows what I'm talking about, are they harmful?
Thanks

[griss]

Lonestar, there are so many slugs/flatworms that exist in our tanks that it would be impossible to ID what you have without a picture. Sorry.