Purge the clams in a bowl of cold salted water for 20 to 30 minutes to release sand, then drain. Scrub and debeard the mussels under cold running water.

Bring a large pot (7.5 L / 8-quart) of well-salted water to a boil for the pasta.

Heat 3 tbsp of the olive oil in a 30 cm / 12-inch high-sided sauté pan with a lid over medium heat. Add the garlic and chili flakes and cook for 1 minute until fragrant, not browned.

Add the mussels and clams, pour in the white wine, cover and steam for 4 to 5 minutes, shaking the pan once, until the shells open. Discard any that stay shut.

Lift the shellfish out with tongs into a bowl and cover to keep warm. Leave the broth in the pan.

Add the cherry tomatoes to the broth and simmer for 5 to 6 minutes, until they soften and the sauce reduces slightly.

Meanwhile, cook the calamarata in the boiling water for 2 minutes less than the package time, until al dente. Reserve 1 cup / 240 ml of the pasta water, then drain.

Add the shrimp and calamari rings to the tomato broth and cook for 2 to 3 minutes, just until the shrimp turn pink and opaque and the calamari turns opaque and tender. Pull the pan off the heat right away, a minute longer and the calamari turns rubbery.

Return the mussels and clams to the pan with the drained pasta. Toss over medium heat for 1 to 2 minutes, adding splashes of the reserved pasta water until the sauce clings to the pasta.

Remove from the heat and stir in the remaining 2 tbsp olive oil and the parsley. Season with salt and pepper.

Divide among shallow bowls, arranging some shells on top, and serve right away.