Another common name for that goby is black-ray shrimp goby.
Scientific name is Stonogobiops nematodes.
There is another goby that looks exactly like the above, only difference is that the dorsal fin is short n stout. Much rarer..Stonogobiops xanthorhinica...Have not seen it in SG before.
Check out this link...shows the 2 side by side..
http://homepage2.nifty.com/PhD-mukai/Labor...onogobiops.html