I had 2 peppermint shrimp. I noticed a few days ago that a piece of a p shrimp was in the tank. Don't know what could have got it. Possibly a bristleworm or maybe my cleaner shrimp or a hermit crab? Today I noticed the other one had disappeared completely. I've had them for a month or two. I've never seen anything mess with them. Water parameters are good. No traces if copper and no medications it treatments used anytime recently. Any ideas??