Petrolisthes armatus, the Green porcelain crab;
Flagler county, Florida (01 July 2019).
Learn more about this species at iNaturalist.org.
Note: Though I’m (mostly) certain this is genus Petrolisthes, I’m not entirely convinced it belongs to P. armatus. It could be another species I don’t know about. In this range, however, and to the best of my understanding, P. armatus is the most likely candidate I know of.