Bring 6 cups water and salt to a boil in a large saucepan over medium-high heat. Add squid; cook 3 minutes or until squid is just tender. Remove squid from pan with a slotted spoon. Plunge squid into ice water; drain. Cut squid into 1-inch pieces. Place squid in a large bowl.
Add shrimp to boiling water; cook 3 minutes or until done. Remove shrimp from pan with a slotted spoon. Plunge shrimp into ice water; drain. Add shrimp to bowl with squid.
Place a vegetable steamer in pan. Reduce heat to medium-low. Arrange scallops in steamer; cook over simmering water 6 minutes or until done. Plunge scallops into ice water; drain. Add scallops to bowl. Cover scallop mixture; chill.
Remove steamer from pan. Add octopus to simmering water; cover and simmer 2 to 2 1/2 hours or until fork-tender (add additional water, if necessary, to cover octopus.) Plunge octopus into ice water; drain. Rub off skin. Cut octopus into 1-inch pieces. Add octopus, lobster, and crabmeat to scallop mixture. Add juice and next 4 ingredients (through garlic); toss gently to combine. Chill for at least 2 hours. Garnish with lemon wedges and parsley sprigs, if desired.