I had this adoreable little (about an inch long) yellow watchman goby. I had it for months in a 30 gallon. I did some rearranging and put him in the big reeftank. About 3 weeks after he was in there, he disappeared.
I assumed either my calliopsis ate him or he just died and the cleanup crew took care of the remains. This was several months ago. Well, he came out when I fed the tank tonight! His home is behind a huge clump of yellow polyps and he blends right in! (Granny needs new glasses) I was happy to see him and he is at least an inch longer now too.