Keep a large kettle of lightly salted water at a near boil for the pasta.

Cut the artichokes in half lengthwise and rub them with the lemon. Using a small paring knife, scrape away the thistley chokes. In a large deep nonreactive saucepan, heat the olive oil over medium heat. Add the artichokes and garlic, cover, and sauté, shaking the pan occasionally, until the artichokes are tender, about 10 minutes. Using a slotted spoon, transfer the artichokes to a bowl and discard the garlic.

In the same saucepan, sauté the red pepper and shallots for 5 minutes until the peppers soften, adding a little more olive oil, if necessary. Add the tomatoes and bring to a simmer, mashing down on them with a wooden spoon. Return the artichokes to the pan, partially cover, and reduce the heat to low.

Place the cleaned clams and mussels in the freezer for 10 minutes while you prepare the sausages. In a medium skillet over medium heat, cook the sausages, turning occasionally until browned, about 10 minutes. When cool enough to handle, slice them into ½-inch rounds, add to the sauce, and cover. Bring the kettle of water up to a full boil, add the pasta, and cook until al dente, about 12 minutes.

While pasta is cooking, raise the heat under the sauce to medium-high and cover for 2 minutes to create a head of steam. Add the clams and mussels to the sauce and cover. Cook, shaking the pan occasionally, until the clams and mussels open, about 4 minutes. Turn off the heat and set aside with the saucepan lid ajar.

Drain the pasta and return to the kettle. Add a ladle or two of the sauce and heat briefly. Divide the pasta among warm serving bowls and top with more sauce and the shellfish.