I've got 2 Thai Micro Crabs in my 10 gallon shrimp/CPO tank. They normally stay completely away from each other. Now, this morning, I see them side by side on my sponge filter. I don't know if they just found the perfect spot and are sharing it, or if they are trying to be close to each other to mate. Whichever the case may be, it's nice to see them for once.