Grapsus grapsus, the Sally lightfoot crab;
Monroe county, Florida (05 July 2011).
I had a devil of a time resolving the identification to this crab, but the consensus on iNaturalist settled on the Sally lightfoot crab, Grapsus grapsus. So be it! Anyhow, this crab was one of many photographed on the edge of Key West. I observed them on multiple visits during the 2010s. A very cool, night-centric species.