Nassarius versus Whelk question

[ozmosis7]

So a while back I picked up these nassarius snails off eBay. They were so healthy I decided to get more. Only this second batch seemed a little more aggressive. I have bare bottom tank and I like to have a few nassarius to dig in the detritus, but these all seem much bigger than what I usually get (about the size of a dime). And I also got a shipment of turbos with these, that ended up in shock it seems or maybe DOA (hard to say for sure). Anyway, a couple of these so called nassarius were inside the shell. So now I'm thinking they are whelks and after some research I believe they are cantharids (Indo Pacific Snails). They don't seem to be harming anything too much, but now I'm worried they might take out all my turbos and ceriths, and could go after shrimp (including my mantis). I've attached a few pictures. Does anyone have experience with these and know for sure what they are, and the risks associated with them?

 

[ozmosis7]

For now, I've moved them to the sump with the mantis shrimp. I'm thinking they won't be able to take him down and if nothing else, he gets a little exercise. If anyone can confirm my suspicions though, I'd appreciate any advice.