I recently got a nerite snail from aquarium co-op, as shown in the image. I have only added the snail and new gravel to the tank. The gravel was dry when I bought it. I have no clue how the baby snails could have got in there. The only plants in the tank are ones that I took out of my other tank, which is baby snail free and has two other nerites. Can someone please explain to me what is going on?