EJ, scholars differ about eating everything you find in the shell. A well cooked crab will yield some backfin lump when you pull the swimmer legs away, and oftem a bit with each leg. The legs themselve are not worth much unless its a VERY large crab.

Unlike Barry the mighty Finn, I don't eat the greenish 'mustard' or gray gills, inside the shell.

Severn has it right above, except I like to crack the shell or carapace in two halves to facilitate retrieving the white flesh of the crab. You should know the latin name for the Blue Crab is Callinectes Sapidus, Beautiful Swimmer.