Ghost crabs were pretty common on the beach. Here's a big one:
The crabs emerge from holes in the sand, scuttle sideways very quickly, and then return to their holes in the blink of an eye. Because they're basically sand-colored, we thought we were seeing things at first!
We found some crab "dens" where their scuttling tracks were quite evident. One day on the beach, I had a good time with three or four ghost crabs, watching the very tips of the eyes emerge from a hidey-hole, then seeing the crab make a run for it. I'm not sure what they were after, although I did see one latch on to a piece of seaweed and run back into its lair.
On the bay side, we saw fiddler crabs. On the Chincoteague end of Assateague, the Park Service had built a wooden boardwalk out through the salt marshes. The ground was crawling with these little crabs. Fiddler crabs are identified easily by their lopsided claws ... probably the origin of their name, too.