Marinated Octopus Salad

Ingredients

• 14 to 16 ounces cooked, cooled octopus (recipe follows)
• 1 small red onion, sliced thin
• 1/2 cup chopped celery
• 1 tablespoon drained capers
• 2 tablespoons sliced pitted calamata olives
• 3 tablespoons extra-virgin olive oil
• 1 1/2 tablespoons good-quality red wine vinegar
• Salt and freshly ground black pepper to taste
• 1 tablespoon flat-leaf parsley, leaves only, coarsely chopped
• 1 bunch arugula, rinsed and dried