I habitutally give inexpensive or "commercial" shells to pretty well
everyone i know, but the greatest surprise that has ever come from this,
came last week, when a friend came up and said "You know those big
shells you gave us a while ago?  Well, we put them in the kid's
aquarium, and now we have a pile of snails crawing around the place!"
Ok, i thought - what the heck is going on?
These were an ancient Charonia and Cassis cornuta from the Phillipines,
so i was puzzled in the extreme, until i saw the critters in question:
Fresh-water snails of the genus Physa.  However, i had had these shells
for a few years, and they had come from an old collection before that -
so assuming that once upon a time, they had been left in a stream for a
brief period of time, and had picked up either "hitch-hikers" or the
eggs of same, it had still been quite a number of years since this was
possible.  Oddly enough, the wee beasties cam in two distinct flavors -
completely grown (over 20mm, after having been in the tank for less than
2 weeks), and rather small (less than 10mm), which indicates that both
eggs and adults had survived in an aestivated form for at least 10
years!! (None have passed on yet, so i can't get a photo, but i don't
recall having seen this species in Nova Scotia, and in any case, Halifax
has notoriously acidic soil and water, being built upon granite and
slate: so, non-marine shell-makers are uncommon, except in gardens and
lawns, where a man-made alkaline condition exists.  So, they could not
have come accidentally from the stream which runs past their house,
which has 75mm spiders, but no Physa that i have ever phound.

I'd like to know whether it is an uncommon occurance for fresh-water
snails to survive in a dormant form for many years, and what is the
longest period known for the revival of same: has anyone ever left an
amphora from King Tut's tomb, for example, in a wash-basin, and found
3000 year-old snails the  next day?

Yours in The Wilderness of the Great White North,
Ross.