Were there flowers on the cabomba, or just leaf buds? I have seen flower buds on cabomba in the store (new from the nursery).
The snail is a ramshorn. Not my favourite, for no particular reason. They lay eggs, so you will probably find egg masses (look like little blobs of gelatin stuck on the underside of leaves, sometimes even the tank walls).
[Just re-read my last post to refresh my memory on this thread, and noticed I mis-typed that I prefer resting during the daylight, rather than testing.
Course, the former is true too...]