My nerite snail is missing.

I've had my nerite snails for around 8 weeks and when I first got them, I got 4. All of them I see regularly other than one. When I first got them this nerite snail didn't move for days but eventually I saw that it was now off of the log it started on and was instead on the gravel right next to the log. The next morning, I didn't see it anywhere and assumed it was hiding under the gravel. After that first week, I haven't seen this snail at all. The tank hasn't smelled like dead snail either. I have no clue what might have happened to this snail because the lid on my tank covers everything really well and there's no way the snail got out.
There are only two possible explanations I can think of
1. I was sold a snail that was already dead
2. For context: there's a hollow cave thing that I have in my tank for my fish and since I got it used, there's a small hole about the size of a nerite in the top. My second explanation is that she got into that hole and has just been living inside of the decor.

 

My first question is what type of nerites are they ? All the same ? Sometimes nerites will leave the tank for a test above the water line , have you checked there ? Most nerites won’t hide under gravel, if any !

Some snails are more quirky than others ! I have a helmet nerite that panicked me by burrowing into the sand ! I’d never seen a nerite do that before but he’s fine now and certainly fast ! He just doesn’t like change.

 

My first question is what type of nerites are they ? All the same ? Sometimes nerites will leave the tank for a test above the water line , have you checked there ? Most nerites won’t hide under gravel, if any !

Some snails are more quirky than others ! I have a helmet nerite that panicked me by burrowing into the sand ! I’d never seen a nerite do that before but he’s fine now and certainly fast ! He just doesn’t like change.

They're all black racers but they each look significantly different so I can tell them apart. I have very little space above the water line and she's not up there. At first I thought she was just hiding and adjusting but now it's been months and I feel like that's an incredibly long time.

 

Yeah I think black racers and helmets are the same just by a different name.. they do burrow. Every time I disturb my tank mine burrows and I don’t see it for weeks. If I go searching I can find him though.

With it being months it’s a possibility it’s died but I would of thought you’d of had an ammonia spike or at least smell the guy ! If you can’t tell them apart maybe you’re seeing different ones ?

 

Yeah I think black racers and helmets are the same just by a different name.. they do burrow. Every time I disturb my tank mine burrows and I don’t see it for weeks. If I go searching I can find him though.

With it being months it’s a possibility it’s died but I would of thought you’d of had an ammonia spike or at least smell the guy ! If you can’t tell them apart maybe you’re seeing different ones ?

All these are why I think it might have just been dead when I first got it, especially considering I only ever saw the shell and not the actual snail. The thing that makes me think there's no way it just died is the fact that there was no ammonia spike and no smell at all

 

I have two nerites, the large one I see regularly at least every couple days. The smaller one, I see for a day or so every couple of weeks. Seems to spend its time under gravel.

 

Since it’s been months, I would suspect the snail died and was eaten, or the snail escaped the tank. However I have had snails go missing for awhile and turn up just fine too, but not for months at a time.

 

In that case, you should find the empty shell somewhere.

 

Update: It was dead. I found the shell buried in the gravel while cleaning
I think it was dead when I bought it because I thought that one looked weird compared to the others and it didn't ever move from the spot I put it in when I first got it.