Bring a pot of salted water to a boil. Add the scallops, reduce the heat and poach gently for about 2 minutes. Drain well and chill at least 30 minutes, or up to overnight.
Stir together the onion, clam-tomato juice, ketchup, lime juice, cilantro, serrano chile and hot sauce in a large bowl. Season with salt and pepper.
Quarter the scallops. Add the scallops and shrimp to the sauce and stir gently to combine. Divide among 4 glasses or bowls. Serve with saltines or chips.
Photograph by Kat Teutsch
Recipe courtesy Marcela Valladolid for Food Network Magazine