First, in discussion of sizes of crabs (micro, jumbo, etc) I have a general idea of what people mean, but I would like specifics on how big each of the different types is. Based on that information, how many crabs will be happy in a ten gallon? I have one crab that is in a Japanese snail shell and is 2-3 in long with shell. The other two are an inch with their shells. I would plan on buying more of the smaller ones.