Lol, welcome to the aquarium hobby!
One of the downsides of buying live plants are snails! Chances are if you buy a fair bit, some of it will have a snail eggs on it. Some times they are visable as long stringy globules on the undersides of leaves, sometimes they are not.
Anyhow, regardless of if you spot them or not, having a planted tank will equal snails at some point.
As Riogal said, give it a day or two and you will have lots. They multiply like there is no tommorrow and usually enjoy a tasty snack (i.e your plants) inbetween!
As for getting rid of them, there are a few ways;
- Natural Removal. The lettuce leaf/cucumber slice method has been suggested - I have never had any luck with this, in the eyes (or stalks?!) of a snail, food is food and who cares about lettuce when they have your plants! Worth a shot though, who knows, what you put in may be ala carte compared to your Vallis!!
- Remove them all. Every morning when your lights come on you should see lots of them on the glass of your tank. No idea why, but thats when they are out and about. Use this as the best time to get your hands wet and get rid of them. Either pull the out, or crush them against the glass. If you do the latter, watch your water stats as as they die, they'll create waste/ammonia etc.
- Treat them with chemicals. There are some treatments out there designed to remove snails. In my experience they do work, usually by killing all the life snails on the first dose, and killing any new ones that hatch during the subsequent re-treats.
However, words of warning, if you decide to use them. Follow the instructions on the pack to the letter they are extremely strong and any overdose or mis-use could have disasterous consequences. Keep an eye on your water stats. The dying snails will obviously contribute to the nitrogen cycle waste as before, but some of the chemicals, if used shortly after some other medicines may start a mini-cycle.
[as an example, this happened to us - used a snail treatment a week (and a water change) after some anti bacterial med. The residue of the med and snail treatment combined and, I found out later, produced an cyanide based derivitive, killled all the friendly bacteria, tank cycled with out us knowing and we lost a couple of fish.]
- Overhaul. Some people on here, have been so fed up with snails that they have temporarily rehoused their fish, emptyed the tank, cleaned the plants, decour and substrate and started again! This is only as good as the clean you do and requires a bit of effort.
- Tank Mates. Snails can make excellent tank mates. For fish that eat them! Clown Loaches, Botias and puffers will all keep any infestation in check and, for the whole, and blimmin' excellent fish. However, they are not the kind you'd just wack in a tank with other fish. If you are going to pursue this line, research the fish and make sure the tank and inhabitants are compatible!
- Au Naturel. You could just leave the tank as it is! They are naturally occuring creatures too!!!
HTH though, I know they are a pain as they spoil what is otherwise a really good tank!