Remove the head and beak from the squid and clean out the insides. Wash under cold running water and rub off spotted outer skin. Cut the tentacles of the squid into small pieces and the body into small dice. Cook in boiling water with the shrimp for a few minutes or until shrimp turn pink in color; drain.

Clean mussels and steam them in a large covered stockpot over moderate heat for several minutes to open them. Discard any that do not open. Remove the mussels from their shells.

Mix all the fish together in a salad bowl. Add the olives, capers and pepper strips. To make the dressing, dissolve salt in lemon juice and whisk thoroughly into the oil. Pour the dressing over the salad and toss. Adjust seasoning with salt and pepper. Sprinkle with parsley and chopped chives, if desired.