What is my pet crab and how do I take care of it?

Most have one claw that is a lot larger than the other. They use the larger claw to tear apart the food and the smaller claw is used to eat, or at least that is what I have came to figure from the three I have had before. I forget the exact name of the ones that I had but they too were brown and sound to be the just like the one you are mentioning. I never had a filter in the tank but I found that it was better to have them in a larger tank (like a 10 gallon or so) so they can have space to walk around. They don't need a lot of water at all, more dry sand actually because a small crab like that can actually drown (something else I didn't know). As for food I would buy crab food not the fish food, different things in both so i'd want it to get the nutrients it needs. If it's a hermit (which most pets are...they're what i'm talking about) make sure there are shells in there that he/she can change to and from when he outgrows his old one.