Yup, these are apple snails, and I think they're beautiful - love the yellow shell
Here's an excerpt from PlantGeek.net about Apple Snails (from this article:
http://plantgeek.net/article_viewer.php?id=14)
"Apple snail (Pomacea bridgesi) - Comes in several different color varieties varying from white to brown. These snails are not plant eaters. They can get up to
softball size [

] and are one of the only types of snail that will eat hydra. Apple snails are egg layers and will have a single large clutch of eggs laid above the water surface. These snails are not hermaphorditic and can be of either gender. They
can't lay eggs without one member of each gender [which is very good if you don't want a snail overpopulation]."