HCA: Hermit Crab Association

Hercules has a strange marking I just noticed on the left side of his body. I looked at my other crabs and don't see it on any of them. Looks almost like it's stretching. See picture below. it's black, close to the opening of the shell. Looks like a few black lines with another line crossing them.

The area you are referring to is the gills and you got a great shot of it. You can see it here also.

That is an awesome picture.