Yup... they were from you. (thank you- I love the Spixis!!!!) There are a lot of accounts of people who have witness Spixis eating other snails - and some of Briggs doing the same... but it seems most don't- which is what makes me wonder if I'm screwing up their diet somehow and they need more protein... there are always veggies available to them.
It's a heavily planted tank (almost no empty spots)- I have:
Shrimp- Ghosts and cherries. (Ghosts maybe responsible)
Fish- Danios, Cherry Barbs, 1 Pleco and Corydoras. (None of these would eat snails)
Snails- Briggs , Spixis , Bladders , MTS , and Quilted Mels. (Briggs and Spixis both possibly responsible although in both cases it is not usual behaviour.)
The tank has stayed steady for several weeks no new additions- the only thing new is the Spixis (and two new briggs- also from you).
The only things in my tank which have been reported to eat other snails are Ghost Shrimp- but they typically only eat the tiny ones- I've been seeing empty shells 5mm-6mm in diameter all of a sudden.
I doubt it is the Briggs- I've read of reliable people on here claiming their briggs were predatory towards smaller snails- but it seems like it is extremely rare behaviour and I've had one brigg for a month with no predation... the others are all pretty small themselves still.
Then of course there are the spixis. Could they be not getting enough protein?
I supopse- since I
HAVE witnessed ghosts eating bladders in my tank- the ghosts could simply have moved on to bigger prey now. Could all be a coincidence.
Or- they could be dying of natural causes and being eaten after they die... no swings in parameters in my tank. Nitrogen is 0/0/10. Hardness is 8/8. pH is 7.5. It's stayed about this for quite some time.
I really don't mind having some of my ramshorns and bladders eaten- it's actually desirable behaviour for me as long as the brigs or spixis don't get eaten... it's just a little bit of a mystery.
Incidentally, I do have another question...
I JUST FOUND SPIXI EGGS!!!!!!!!
That was record timing... took less than a week for them to get in action.
I noticed them doing the deed this morning and then this afternoon I have a big glob (the size of the spixi herself) hanging from the red Ludwigia... Fascinating how each egg can be seen individually with a little white dot inside each.
They are transparant- (no they're not ramshorn or bladder eggs I know what they look like) - is this normal- are they fertile? I thought most apple snail species did not lay transparant eggs?
I seperated them from the tank into a small container for now... unfortunately I can't use the breeder net because it is housing baby dwarf crayfish at the moment. (that and Qulited Mels occassionally climb up onto the lid- and I already have had a couple drop into the breer net... don't want QMs eating the eggs).
Will they be OK in a seperate container or do they need water movement. I can do twice daily water changes until they hatch that's no problem. I had to seperate them because the ghost shrimp kept trying to eat the eggs.
Quite an exciting day- noticed my first berried cherry shrimp just a few minutes ago too.
First spixi sex, spixi eggs, and berried cherry shrimp all in one day- what more can an aquarist ask for?
LOL... I'm overly protective of these eggs... wonder if I'll be cursing the eggs in a few weeks time if they lay like crazy...
) they do not eat or pick on any other snail , I have never seen a spixi eat a snail, of any kind. 
