I can't really give you an ID with that pic. It kinda says to me G. ternatensis, but thats just a tiny guess. Would need a pic of the meral spots to really tell. At any rate that baby won't be able to hurt anything except maybe nass snails. You can put him back in your tank if its a reef tank. it will grow very slowly, but it could be a threat as an adult. Or you could put it in a 5-10 gallon tank with a small powerhead and weekly water changes, and feed it tiny pieces of marine flesh like krill or shrimp once every 2-3 days. You might be able to train it to eat pellets and the like too. They are very interesting. Good luck!
Dan