The likelihood is they are malaysian trumpet, ramshorn, or pond snails. Those are the most common "pest" or hitchhiker snails.
If you aren't a fan of snails, it is best to remove them now. They're not normally harmful, but their populations can explode if there is a food source. As a result, most people will consider them pests.
There are not many fish that will eat them, that are also acceptable for most setups. Loaches are the most commonly suggested fish to eat them. All loaches that will eat snails do best in groups, or are aggressive. Clown loaches are too big for the vast majority of tanks (they can reach 12 inches in length or more, and commonly reach 8-9 inches). Puffer fish will also eat them, but are quite aggressive and require snails or similar hard shelled invertebrates to eat.