What are some different types of aquatic crabs?

I know about the common fiddler crab, the red clawed crab and the vampire crab. I am looking for other types(colors) of crabs. Several pet stores told me that a lot of the crabs are the same type they just have different colors. Can anyone give me a list of types of crabs? Preferably on the small size. 4 inches and under. Plus if anyone can give me a website that has information about the crabs that would be great. I know it was hard to find any real information about the vampire crab. I know the general care requirements for them(need air, salt in water, good escape artist, etc). Does anyone know how they are with slow moving fish or kuhli(koolie)loaches? I keep reading controversial things about whether they can get along or not. Right now the fish are only about the size of a large marble(1.5-2 inches long and about 1-1.5 inches round) but they will grow up to be about 5-6 inches. most of the loaches are about 2-3 inches long. I read vampire crabs stay around 3 inches small so something around that size would be great.