This is a Spiny Lobster. Its colors are vivid, with a deep shade of purple on its arms. Richard emailed me with his own experience, which follows: "I really never fed it anything specific; it would eat flake foods, pellet foods especially anything that was meaty (would go crazy with chopped up shrimp, scallop or pre-packaged frozen foods). It would only go after weak fish, but never healthy ones. I had to be careful introducing new fish. Most behavior was nocturnal; during the daytime it would usually only will come out for feeding. The lobster would shed about once every 6 to 8 weaks, it never got larger than 3 inches approximately." Reef-safe-ish. :)
Another friend of mine had one of these living in his reef, and the day he had to break down the tank he discovered a large collection of his plastic feeding clips squirreled away in the lobster's den. How funny is that?