If using salt-packed anchovies, rinse them under cold water. With your fingers, pry them open along the back and lift out backbone to yield 2 fillets. Rinse fillets again to remove any fine bones; pat dry on paper towels. If using anchovy fillets in olive oil, lift out of jar or tin, leaving oil behind (no need to rinse oil-packed fillets). Finely chop 6 fillets; set aside. Cut remaining 6 fillets into 4 or 5 pieces each; set aside.
In an 8-qt. pot, bring 5 qts. well-salted water to a boil over high heat. Add pasta and cook, stirring occasionally, until tender to the bite, about 10 minutes.
Meanwhile, put olive oil, garlic, finely chopped anchovies, and chiles in a deep 12-in. frying pan (with at least 2-in. sides) or wide pot and cook over low heat, stirring, until anchovies dissolve. Stir in parsley and remaining anchovies; turn off heat.
When pasta is almost done, set aside 1 cup of the cooking water, then drain pasta and transfer to pan of anchovy sauce. Toss quickly until all the strands are well coated. Add some reserved cooking water if pasta seems dry. Set aside 2 tbsp. bread crumbs, then add remainder to pasta and toss again.
Divide pasta among 8 warm bowls and sprinkle each serving with some reserved bread crumbs. Serve immediately.
Note: Nutritional analysis is per serving.
Italian grocers and specialty stores carry whole salt-packed anchovies, typically sold by the piece, which are meatier and more flavorful than oil-packed.