Every Christmas eve, we eat crab as a family. Generally there are about 8 to 12 of us. So either me or your mom goes out and gets four-six Dungeness Crabs. We then clean them up, put all the legs in one bowl, and cut the bodies in half, and put them in another bowl. Then everyone gets half a body and a few legs. We use special tools to pick out the crab meat. When everyone has cleaned as much crab as they like, we all make crab salads. Mimi (my grandmother) makes Thousand Island dressing using mayonnaise, ketchup, and relish. Then you put the crab on your salad, put dressing over that, and have yourself a meal!
My father carried on this tradition from his family. He has eaten crab for dinner for as long as he can remember. He doesnt know why or how the special food of choice became crab. He moved around a lot, but never lived anywhere coastal. For much of his life he lived in southern California.
I think crab developed as more of a specialty food than anything else. My family has never eaten a lot of seafood, and the only time we ever eat crab is on Christmas Eve. I think this exclusivity makes it a specialty food, at least for our family.
I dont think there is a lot of symbolic meaning behind the fact that it is crab. I think the reason why it became a tradition is because it is more of social activity. It takes 20 or 25 minutes to clean all the crab out of the body and legs, and creates a good social environment instead of just sitting down and eating.