The soft-shell crab po' boy is the only one in the family where the filling does not fit the bread, on purpose. A whole soft-shell crab is fried and laid in the loaf intact, body, legs, and claws, so it overhangs both ends and the sides, legs jutting out past the crust like a thing that escaped the kitchen. You eat the entire crab, shell included, because at the soft-shell stage the molted shell is thin and edible and crisps in the fryer along with everything else. That overhang is the defining image and the defining eating problem: the sandwich is built around a creature, not a portion.
The craft is in the fry and in arranging an awkward shape so it can be bitten. The crab is cleaned, dredged in a light seasoned flour or cornmeal coating, and fried hot and fast so the thin shell and the legs crisp while the body stays moist and sweet inside. It goes into the loaf still hot, set so the body sits over the crumb and the legs hang clear, because a soft-shell crab steams its own crispness away quickly once it is enclosed. The thin-crusted, glass-crackly New Orleans loaf is chosen because it shatters cleanly under a bite that already has to manage a crab leg, and because its airy crumb cushions the body without crushing it. Dressed means shredded lettuce, tomato, pickle, and mayonnaise, frequently a remoulade, applied as the cool, acidic counter to a rich, faintly briny fried crab. It is a seasonal sandwich tied to the soft-shell molt, and a po' boy shop builds it to order so the legs still snap.
The variations are narrow because the crab dictates the form. A remoulade dress is the standing local choice; a half-shell or split build makes it easier to eat at the cost of the whole-crab drama; a richer Creole-spiced dredge leans into the heat. Those readings, along with the rest of the po' boy family of shrimp, oyster, catfish, and roast-beef debris, are their own sandwiches and deserve their own articles rather than being crowded in here.