Could they be zebra nerites, Neritina natalensis? The size matches (and the claim that they won't grow bigger than that, but we all know how reliable fish stores might be when they talk about sizes...) and they are absolutely the best algae eating snails I've ever seen. They really blast the algae off the tank walls.
Oh, and my MTS eat only fish food, some algae and only rotting plant parts. There has been cases when they have eaten live plants (or so some people have said), but it is really rare and might happen because they have nothing else to eat or there are too many of them (so, not much to eat) or then they just get blamed of someone elses munching or actually are munching the plants for no specific reason. But I have never seen a live plant eating MTS.
They are also easy to keep in control, when the lights go out they climb to the tank walls and you can just net them and either kill them or offer them to someone who might want them. I don't usually see mine much, they spend most of the time buried inside the substrate and I have never had too many MTS in my tanks.
Oh, and my MTS eat only fish food, some algae and only rotting plant parts. There has been cases when they have eaten live plants (or so some people have said), but it is really rare and might happen because they have nothing else to eat or there are too many of them (so, not much to eat) or then they just get blamed of someone elses munching or actually are munching the plants for no specific reason. But I have never seen a live plant eating MTS.
They are also easy to keep in control, when the lights go out they climb to the tank walls and you can just net them and either kill them or offer them to someone who might want them. I don't usually see mine much, they spend most of the time buried inside the substrate and I have never had too many MTS in my tanks.