You can see the shrimp in post #26, doesn't look the same for me, but hard to tell. (google mini japonica: i can't seem to find a species name or origin)
The Stiphodon do bury themselves under the stones, but in my case, sand and large river rocks/pebles i haven't encountered a problem. They seem to create some hideout under an edge, but don't move enough material to dislodge any of my stones. This might be due to the size of the stones (large) or the substrate (sand) which doesn't make it easy to do large excavations without falling "back".