Peel shrimp. Make a shallow cut lengthwise down back of each shrimp; wash out vein.
In 12-inch skillet or 4-quart Dutch oven, melt butter over medium-high heat. Add onion; cook, stirring frequently, until tender. Reduce heat to medium. Add shrimp; cook uncovered about 8 minutes, turning once, until shrimp are pink. Remove shrimp from skillet; keep warm.
Add champagne to onion in skillet; cook until liquid has evaporated. Stir in rice. Cook uncovered over medium heat about 5 minutes, stirring frequently, until edges of rice kernels are translucent. In a glass measuring cup, mix chicken broth and clam juice; pour 1/2 cup mixture over rice. Cook uncovered, stirring occasionally, until liquid is absorbed. Repeat with remaining broth mixture, until rice is tender and creamy.
About 5 minutes before risotto is done, stir in shrimp, arugula, cheese and pepper. Sprinkle with parsley before serving.