Soak the mussels and clams in water for an hour. Discard any broken mussels or clams, or open ones that don’t close when tapped on the work surface. Under cold running water, scrub the mussels and clams thoroughly to remove any grit, pulling out the beards from the mussels.
In a large deep frying pan over a medium heat, sweat 1 clove of the garlic in 2 tablespoons of the oil. Increase the heat to high, and add the mussels and clams with half of the wine. Cover with a tight-fitting lid, and cook for about 5 minutes until the shells are open (discard any that remain closed). Remove from the heat and discard the garlic.
Slice the squid into rings and finely chop the remaining garlic. Heat the remaining oil in another pan, and sauté the garlic, parsley and chillies for a few minutes. Add the squid and cook until the edges curl.
Pour in the remaining wine and cover. Cook for 10 minutes. Add the shrimps (just the tails) and cook for a few more minutes before adding the clams and mussels. Simmer for another few minutes, then remove from the heat.
Meanwhile, bring a large saucepan of salted water to the boil, add the spaghetti and cook until al dente. Drain and add the seafood mixture to the spaghetti, mixing well.Stir over a low heat for a couple of minutes. Serve piping hot.