I had a pink/blue spotted shrimp goby, and it is a carnivore. make sure you feed it 2-3 times a day shrimp, clam, crab, etc. it will get to be about 4-5" long, and is more aggressive than other shrimp gobies.
12 gallons will be fine, those things are mean now. Feed is twice a day with fresh food, perfurabley. I would get it a shrimp goby to be its friend. With out the shrimp, it will not be able to dig burrows as well, plus, you will miss out on some intresting behavior without a shrimp.