This little guy is the answer to the burrow puzzler, part A. You can tell this is a male fiddler crab by the one large claw which is used to wave at girl fiddlers in an attempt to lure them to his burrow to see his etchings.
B part answer: The little balls are produced by the fiddler feeding on detritus and other organic material in the marsh mud.
Thanks for playing.
Don't be crabby if you didn't get this one right, there will be more.