Ramshorn snail. Considered a pest snail because they breed. They eat fish eggs and plants if they get hungry. They come in as eggs on plants. The eggs look like small clumps of clear jelly with little dots in.
They will breed out of control if they have plenty food. This means uneaten fish food and dead plant matter. If you take care not to over feed the fish and remove dead plants immediately there shouldn't be a snail population explosion.