I've never seen a snail quite like that before. The nearest I can think of is an apple snail, Pomacea diffusa.
Some of the photos are missing from this thread but if you compare your snail to the photos which are still there, you might be able to ID it.
(Thread rework in progress - please pardon our dust!) Freshwater Snail Species In The Hobby (Two Clea helena assassin snails and a Planorbid ramshorn - photo by CassCats) Index Basic Terminology for Identification Physidae: Bladder Snails and Tadpole Snails Lymnaeidae: Pond Snails...
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