Ok, seriously, I thought these were ALGAE eating shrimp-- I'll admit that they usually do a good job cleaning up, but of late, they've been a terror in one of my 5g. At the moment, two of them are munching on yet another ghost shrimp that I watched them ambush and kill (I really don't know how many that makes,) but I've also seen them kill a butterfly loach (sad too, because he was really cool,) along with baby guppies, and even smaller yamato-numa-ebi. I'll post a picture soon, if I can get them to come out of their little grove, but I'm about 100% certain that these are just Caridina japonica- the've just gotten really big and lazy.
So, the question is, have any of you had this problem before, or did I just end up with the Manson family of the invertibrate world?