This guy is an Arrow Crab. Originally I bought one because I was tired of all the bristleworms in my tank, his favorite meal. However, I had a Coral Banded Shrimp and he killed the Arrow Crab relatively quickly. After many years, the CBS died, so I got a new Arrow Crab. Mainly I enjoy this creature because of its delicate structure and blue pinchers, and because it is not a crab that likes to hide. Some report it will kill fish, but it would have to be smaller fish if at all. I've never had any negative experiences. Reef-safe-ish.