Cover the shrimp shells with water in a saucepan. Bring to a boil, and then reduce the heat and simmer to create a shrimp broth, about 20 minutes. Strain.
Heat the oil in a large, heavy-bottomed skillet. Add the shrimp, squid, sofrito, gilthead, langoustines and mussels and cook for 3 minutes. Remove the seafood from the pan and set aside. Stir the rice into the juices from the seafood in the pan and saute for 1 to 2 minutes. Pour over the shrimp broth and red sauce and return the seafood to the pan; stir together. Cover and cook until the broth has been absorbed and the rice is cooked through, 15 to 20 minutes.