I have a maroon hermit crab (I believe that is what he is) and a pincushion urchin in the same tank. My urchin is very dear to me and the crab is killing the urchin. He will go up to the urchin and rip his small tentacles and lots of spines off. I stop this whenever I see it, but my urchin has already lost a lot of spines and tentacles. I can not get rid of either and do not wish to injure the crab (which people have told me to do, but that’s just messed up) I am trying to keep them separate, but they are both living creatures that will move when they want. Any help would be appreciated.