Astrea Snails with Scraped Shells

[infuse]

I have been setting up a reef aquarium for the past few months. I have a cleaning crew that includes about 15 Astrea snails. About two weeks ago I noticed what looked like white marks on a few of their shells. At first I thought it might be die-off of whatever was growing on the shells when they were purchased. Since then I've noticed that about three quarters of the snails have white marks on their shells. I plucked one over to the glass to get a good look and it appears that the shells are scraped or ground down. The scraps are in a random pattern and usually on the top half of the shells. I haven't found any empty broken shells although a few of my blue-legged hermit crabs seem to be wearing new Astrea shells - not scraped though. I'm trying to figure out what is happeneing. I have two peppermint shrimp, a few rogue crabs that I have been catching, and a few small bristle worms in the sand. I also have a very small (4mm) pistol shrimp that I haven't seen in months although I do hear occasional individual popping noices in the night. I have no fish in the tank yet. Does have anyone have an idea of what is happening?
Thanks.

 

[tizzo]

Any chance you have a mantis shrimp?? Even if it's small.
Try putting some food in late at night, and observe under moonlights or a flashlight and see if one comes out...

 

[natureboy]

My bet is on one of the unidentified crabs

 

[puffer32]

Or your pistol shrimp you haven't seen in months is dead and you are hearing pops from a mantis :notsure:

 

[reefiness]

i think that you should try really hard to find out the source of that pop, when i had a mantis, i remember jets of sand coming out of the holes in the rocks as he went in an flapped around in there. also when i had a mantis, the sound seemed to be coming from a different location night, and pistol shrimp usually stay in one spot as i have heard.

 

[infuse]

Thanks for the advice. I'll try to determine if I have a mantis shrimp and will keep on catching the crabs.