In a heavy nonreactive 36 cm skillet, melt the butter. Add the onions and celery and cook over moderate heat until translucent, about 5 minutes. Add the garlic and jalapeno and cook for 2 minutes. Add the flour and cook, stirring constantly, for 5 minutes.
Stir in the tomatoes and their juice, the paprika, salt, black pepper and cayenne. Bring to a simmer, cover and cook for 5 minutes. Add the shrimp and stir until they curl and turn pink, 2 to 3 minutes. Stir in the scallions and parsley and serve over rice.