Looking for suggestions on catching a "night monster"

So, every 2-3 days I find a new empty snail shell with an almost invisible mucus bubble around it that collects sand and debris. I always make the new discovery in the morning.


I think I've found what the "night monster" is by researching this mucus bubble. I'm 99% sure I have a snail eating flatworm, which is a polyclad flat worm. Fortunately my clams are not in this tank, because it appears they'll go after those too. Sounds like they're incredibly difficult to capture. I have no idea if there's any way to remove this thing, which I have never actually seen. I'm not exactly nocturnal and this thing surely is. I have looked up pictures and videos of the spotted, creepy creature.


Anyone ever catch one of these?

 

Yes, I've seen many pics and vids and I that's exactly what I think I have! It reminds me of a leech and gives me nightmares. So creepy to think about it living in secrecy in my tank. It took me a couple months of missing snails to do the research to figure out what would be causing snails to die. I have to keep my favorite snails in my biocube now. What a pain!


I would totally move the rock out except I have about 50 rocks in my tank, all of which are covered in corals, and I have NO IDEA which rock it could be in. I can guess which side of the tank it probably resides in due to where I find most of the shells, but as I mentioned, I have never even seen this thing.


So how do I find out where a creature lives that I cannot see? A trap I think is my best bet, but I have yet to hear of any trap that's been successful in luring one in. I have a feeling I'm going to be feeding this thing snails for years to come at this rate....

 

I have considered that, however I have a few problems with that idea:

#1. I'm not sure how I would make a trap with such a small opening, yet I could fit a clam in there. A small pop bottle wouldn't have a big enough opening for the size of snails he's interested in, or be big enough to fit a clam in. It almost needs to have a door to fit the food item in, and that's where it starts getting really tricky. Not that I would be against going through the effort of creating something IF I thought it would work. I suspect it wouldn't because he has lots of other things in the tank to prey on, he's probably not going in a tiny bottle opening. My sharknose goby would be all over it though I'm sure!

#2. This thing is nocturnal. I am not. Seriously. This might sound funny, but I think my grandma stays up later than I do. I have no idea how I could possibly sit watch my dark tank every half hour without falling unconscious. It only comes out in the middle of the night. I suspect late in the night, because on a couple occassions when I did get home late, I checked the dark tank to try to find this thing and I cannot find it anyhwere, yet there has been a snail shell victim by 5:30am when I'm up. However, it doesn't happen all night.

I swear, this is impossible. There probably is no real solution, but I'm still open for any ideas. Winner gets to keep it if I catch it! lol

 

Well, I ordered from Reef Cleaners a couple months ago, so needless to say he has a huge supply of snails. For that reason he may not go in a trap, but I still think that's my best chance too. Hmmmmm and I could put it near where most of the snails are found so it's an easy target. Now I just have to keep watch on the tank all night, maybe talk the family into working shifts! Sadly when you live far away from civilization like I do internet is not easy to get and all options I have are capped, so live streaming isn't possible. I would love to have streaming of my tank to keep an eye on it.

I really want to see this thing. I might freak out if it's gigantic.