Carefully wash the mussels and clams and cook them in a saucepan with no water until they open. Shell the mussels and clams and put them in a pot. Boil the octopus, squid and prawns separately. The prawns must be peeled and cut into pieces. The octopus and squid must be chopped into small pieces. Place in a dish and add olive oil, salt, pepper and lemon juice (or a few drops of vinegar). Stir the sea food salad to absorb the seasoning.