What Could Be Killing My Assassin Snails?

[r.w.girard]

Early this week a found one of my two assassin snails, Clea helena, dead in the back of my tank, and this morning the second. Since I put them in the tank a month ago, I have seen no aggression towards them or towards any of the other snails in the tank, except when the Clea helena were eating the other snails.

The list of possible suspects is as follows:
Fish:
a breeding pair of Bolivian rams, Mikrogeophagus ramirezi;
a male Dwarf Gourami, Colisa lalia;
a school of Green Neon Tetras, Paracheirodon simulans;
a school of Hengel's Rasbora, Trigonostigma hengeli;
Snails:
one large and several young Ivory Mystery snails, Pomacea bridgesii;
two Clithion diadema;
a Vittina semitonic;
a Nertina natalensis sp. "zebra";
a plethora of Malaysian Trumpet Snails, Melanoides tuberculata;
Shrimp:
three Amano shrimp, Cardina japonica.

Any ideas if any of these would attack and kill Clea helena? The Cardina japonica, as I have witnessed, have eaten the bodies of the dead Clea helena. But would they be capable of killing them? And if so, why them and not, say, the Melanoides tuberculata?

 

[The Taffy Apple]

If it is anything similiar to how my Assassin snails died then it maybe down to malnutrition... i was simply so focused on not over-feeding my stocking that my little fellas didn't get the diet that they needed. They died overnight within a week of each other and were half eaten by the morning by my shrimp and Corys.

Terry.