[Dolf]

From what I reacall reading Tonga Nass. usually hatch as crawling snails. They usually either get eaten or starve (I don't know that they eat what adults eat right off the bat.) Having said that, when you look at what Dr. Ron says about snail larvae it makes me think that the Tonga Nass. may not be just one species and that perhaps some would have no chance as they would be born floating in the water column. (Yes, I realize that he is addressing a different type of snail altogether in this quote, but I can't honestly recall if all Tongas are the same or not- meaning how their young hatch..)“ What happens is somewhat unpredictable. One needs to have some experience with particular species to know what they will do. Sometimes developmental patterns are predictable from "near-relatives," but sometimes, particularly in species that come from large groups (such as the ceriths where there are over 100 species), different developmental modes are found.

Many of the species that are doing what yours are doing, hatch as small crawl-away juveniles. Others hatch as swimming/feeding larvae. One species I worked on (Oenopota levidensis) spent as long as 55 days in the egg capsule and then hatched to spend as long as an additional 108 days in the plankton feeding. So the total developmental time could be as long as 163 days
“

So, the long and the short of it is that it appears that, if nothing else, there is a chance that a few out of thousands might survive depending on what you have in your tank to eat them. Sorry it is not much help- but I doubt that anybody will be able to assure you that some of yours will survive or guarantee that they will all die.