Mystery snail identification?

I read the sticky note at the top of this forum, and I think it listed two different kinds of snails that are commonly called mystery snails. I can't tell if either one of them looks like my new snail.
(Apologies if these pictures are duplicated. My phone is doing strange things.)

What happened: I have been feeding my goldfish a lot of leafy greens, which they seem to enjoy, but it makes a lot of detritus in the water. Today I went to the LFS and ask if there are any snails that would live happily with goldfish and clean up their leftovers. The guy said mystery snails would be a good match. He only had one such snail in the store, so I decided to take it home and if it does well I can get some more when he gets more in stock in a couple weeks.
So right now the snail is still in its baggie from the store, inside a jar, getting acclimated to my goldfish water a little at a time. This first one is going into my basement pond with my 7-year-old "garbage fish" (found discarded, in baggies of filthy water, in a trash can at the fairgrounds the day after the 2013 New York State Fair ended). It's an approximately 420 gallon pond housing nine common and comet goldfish. Questions:

1. Is this snail really a good match for these fish in this pond?

2. How many such snails would be a good number for this pond? (I am assuming the snails will not overpopulate the pond, because the fish will eat any eggs or babies they produce. Only larger snails will be safe. Am I right about that?)

3. I would also like to put some snails or other cleanup crew in the aquarium with my disabled goldfish (two with tailfin or spine damage that affects their swimming, one with no eyes). That tank has only sponge filters, to avoid injuring the weaker swimmers, so it gets more crud. But I put salt (plain uniodized sodium chloride with no additives) into that tank, about 1 tablespoon per five gallons, refreshed when I do water changes. Will this kind of snail be okay with that? If not, is there anything else that would like to eat leaf bits in the tank that has salt added?

Below are some pictures of the snail, still in its bag from the LFS, and that bag inserted into a jar to keep it upright during water acclimation. And here are a couple of videos, one of the snail climbing up the side and then dropping back to the bottom (I think it got discombobulated by a fold in the plastic bag), and the second, only minutes later, of it trying again and successfully navigating a bag fold to reach the water line:

If at first you don't succeed....

...try again!

Also, is that a tiny second snail on the "rim" of its shell, visible in the first video? If so, how should I care for that little one until it's big enough to be safe from being eaten by my fish??

The mystery snail may eat any plants, but should be a good tankmate for goldies. I got an apple snail in with my goldies and theyre all very happy. All plant munching monsters

The tiny snail... looks either like a Malaysian trumpet snail or a baby assassin snail.

If its an assassin snail you don't want it with the mystery/apple snail as they've been known to still manage to take them down, just not worth the risk.

Assassin snails have black and yellow stripes like a wasp or bee.

Trumpet snails are beige-brown, no yellow or bold black stripes.

So that really is a second snail hitching a ride on the first snail? And it's not even the same kind of snail??
I can't tell what color the thing is. I can barely even see it. In fact right now I can't see it at all. Apparently it moved.
So just what kind of mystery snail is my mystery snail? The LFS guy said it is not an apple snail. He said apple snails are illegal in this state.

NCaquatics said:

Assassin snails have black and yellow stripes like a wasp or bee.

Trumpet snails are beige-brown, no yellow or bold black stripes.

Click to expand...

Okay, when I took the mystery snail out of the bag and put it into the pond, the piggyback rider remained in the bag. So here it is. It's tiny--about the size of a comma in newspaper font. The lines on that note paper are about half an inch apart.
What should I do with it?? For tonight I am putting some water from my pond into the bag from the fish store and letting the tiny whatever-it-is spend the night alone in there.

Thats a trumpet snail. You can choose to release it in the pond or keep it in a small jar of pond water for the time being til it grows... or dispose of it since some people don't like "pest" snails. It will likely breed more.

NCaquatics said:

Thats a trumpet snail. You can choose to release it in the pond or keep it in a small jar of pond water for the time being til it grows... or dispose of it since some people don't like "pest" snails. It will likely breed more.

Click to expand...

Thanks. So it isn't dangerous to my goldfish or to my bigger snail?
What does it eat?

Nope its harmless. They will eat whatever waste the fish miss, dead plant bits. Usually trumpet snails live under the substrate and come out at night. They will aerate sand with their burrowing which is great for plants.

I'm no snail expert I'm afraid, just wanted to say that your goldfish set up sounds amazing! And that those fish were incredibly lucky that it was you who found them! From feeder fish, to thrown away in bags of ammonia water, to several hundred gallons of luxury... nice!

NCaquatics said:

Nope its harmless. They will eat whatever waste the fish miss, dead plant bits. Usually trumpet snails live under the substrate and come out at night. They will aerate sand with their burrowing which is great for plants.

Click to expand...

I quit throwing away money on live plants years ago. The goldfish either devoured or repeatedly uprooted everything I tried planting. Now they get leafy greens and broccoli in leaf clips, nothing growing. It's detritus from the greens that I'm hoping the mystery snail will eat.
So, what do you think about the mystery snail? What is it really? How many of them would be a good population for that pond (again, about 420 gallons, seven common and two comet goldfish, in the basement so it gets chilly but not frozen during winter)?
And can this type of snail tolerate salt at about one tablespoon per five gallons? That's what I have in the aquarium for my disabled fish. If that kind of snail won't do well in that tank, what else could I add to clean some of the debris? That tank has only sponge filters because HOB filters would create too much turbulence and potentially even suck up and kill the weak-swimming fish. But the sponge filters don't do such a great job of catching crud.

Unfortunately nothing eats poop.

A good gravel vacuum could help with reducing some though.

I dont know longterm for salt for the snail Unfortunately. But you could have a fairly good population. They will love the same foods the goldfish enjoy too.

Jim Sinclair said:

So, what do you think about the mystery snail? What is it really?

Click to expand...

It cannot be identified. That is why it is called a mystery snail. Embrace the mystery, young grasshopper.

NCaquatics said:

Unfortunately nothing eats poop.

A good gravel vacuum could help with reducing some though.

I dont know longterm for salt for the snail Unfortunately. But you could have a fairly good population. They will love the same foods the goldfish enjoy too.

Click to expand...

It isn't poop I want eaten, it's leaf debris.

Then yes they will eat any loose leaves

Well, the snail didn't like my pond. And the pond does NOT get salt. But apparently it was too cold in the basement. The snail didn't move for about two days and I thought it was dead.

I put it into a jar of water from the pond and put it outside on the front porch on a warm sunny day. A couple hours later the snail was climbing up the side of the jar.

I called the LFS where I got it. Discussion involved whether the snail could tolerate the salt added to the tank with the disabled fish in it. That tank is in the living room, so warmer than the basement. LFS guy and I came up with a plan to do two subsequent 33% water changes (so about a week, as I do water changes twice a week) without replacing any salt, which would bring the salt concentration in the tank to about half of the current 1 TBSP/gallon, and then going forward add only 1/2 TBSP/gallon when doing water changes.

Meanwhile keep the snail in a separate jar, upstairs so not cold like the basement, and with no salt.

After the second tank water change, when salt concentration is down to about 1/2 TBSP/gallon, do a gradual drip acclimation for the snail, watching carefully for signs of distress. If no distress, snail can be added to the special needs tank.

Meanwhile every night I have been bringing a container of pond water from the basement to the room the snail is in, so overnight it warms to upstairs-room temperature, and the next day doing a couple of partial water changes of the snail's jar using that unsalted pond water.

Well, we didn't need to wait a week for saltless water changes and drip acclimation. When brought back inside and placed in the living room beside the tank, the snail resumed acting dead. Even floated at the top of the jar for a while. I don't know the water temperature in the living room, but according to the thermostat, the room temperature is about 67.

I brought the jar with the dead-looking floating snail up to the second floor (where there are no fish) and put it in the warmest room of the house (windows on both south and east sides), where the temperature is about ten degrees warmer than in the living room.

The snail stopped floating and resumed sticking on the side of the jar, occasionally moves around a bit, but mostly stays in its shell. It ignores blanched leaves (which I removed after several hours to keep it from fouling the water) and an algae wafer.

I think this snail really wants to be in a warm tropical tank.

The store will take it back, but won't be open again until Tuesday. And then the store might sell it to some other clueless person who isn't aware that it's a tropical snail. I wonder if I can rehome it locally?