Atlantic marsh fiddler crab (uca pugnax)
From Wikipedia-
Distribution
Uca pugnax is the most common species of fiddler crab on the east coast of the United States. Its natural range extends from Cape Cod to northern Florida.[2] In 2014, its northern limit was extended to Hampton, New Hampshire, as a result of a range expansion possibly due to climate change.[3]
https://en.wikipedia.org/wiki/Uca_pugnax
Good Morning Gloucester 
The true one clawed bandit, great capture thanks for sharing…:-) Dave & : Kim 🙂
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