Nassarius snails or something else

[MixedFruitBasket]

I did an order of Nassarius vibex snails from a seller I've bought from before, so I'm confident he knows his snails. However, this last batch is displaying a very strange behavior from all the other times I've had this kind of snail.
1: They don't appear to want to bury in the substrate, instead they actively move about the surface hunting or park it on a rock and lurk.
2: Climb on the glass during daylight hours.
3: Climb on the glass at night (not breeding just chugging along like an astrea would)
4: I'm pretty sure they have killed several of my large certh snails.
5: I have also had several previously alive, but dislodged from their rocks clams, wind up stripped clean from their shells. Now, they could have been on their way out maybe, but these were clams I pulled off of rocks when I had to move them so they were very much alive.

Any thoughts?

 

[Proteus Meep]

Sounds like they are predatory whelks...there is one species that looks exactly like the friendlier nassarius......i would remove them