Gobbies with Serpentine Star?

As a general rule it is doubtful that the serpent starfish captured your goby.  The starfish would have to be very large 10″+ to catch something like a diamond sleeper goby or something of similar size.  While not ruling out the possibility if you feed your starfish small bits of clam, krill, or other meaty foods it will accept them readily and keep it happy and fed.