Well, its a little guy about the size of a nickle. He must have been in my tank for about one year since I havent purchased anything that he could possibly hide in. Ive never seen him swim, actually Ive never seen him until I found him dead when I was having temperature issues with my tank. It sure dose looke like a calico crab. I really don't think he was eatting my zoanthids but I did find him laying on my fairy dust palys dead and if he was eatting my fairy dust palys I wouldnt have notice since they grow like weeds in my tank.