There just little snails, im not sure what there called but there are loads in my tank, If you bought some plants recently they would prob have come from that. Fish shops put them in there tanks. They are completely harmless.
cheers.
Some great info here if you hadn't already spotted:
http/www.fishforums.net/index.php?/topic/277805-hitchhikers-in-freshwater-tanks-ponds/
You can quickly get overrun with these free-riders, so as already posted you can get Assassin Snails, but if you plan to keep other snails the Assassins are out, so I suggest picking them out a destroying them as soon as you spot one.
Best from a happy Blue and Red Apple Snail, Zebra Snail, Chopstick Snail, and Yellow Stripe Clam keeper
My assassin snails have started eating each other. I'm quite disturbed about this, since they cost me money and there are still plenty of pond snails that they could be munching on.
we found a snail today too.
They look cool i think, one or two dotted about the place.
But this is because we recently bought some plants from out LFS.
Would be nice to get some pretty snails in there...