Sort of related. I bought an engineer goby a few years ago as a juvenile and it went missing almost immediately. I spotted him after about 6 months, long having assumed he hadn't made it. I thought it was an eel for a moment.
If you aren't familiar, engineer goby's look pretty different when you compare juveniles and adults. He was probably an inch long when I put him in the tank and probably 6-7 inches long when I found him again.
I've learned that diggers can be very shy.