Any idea what these are?

Hooked Newbie

Today will be yesterday tomorrow
May 25, 2007
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Georgia
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Len
They're semi-transparent and "sluglike". They move rather quickly and the rounded portion appears to be mouthlike in that they seem to open and close while undulating forward. Anyone know what they are and if they're harmful at all? They seem to be prolific.

DSC_0045.JPG DSC_0046.JPG
 
Are they tiny snails?
 
The little things above and below the snail? They look like some form of flatworm. Hard to tell with that picture though. Click.
 
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