Mix together the curd cheese, cream cheese and mayonnaise until a homogeneous mixture is formed. Drain the tuna and anchovy rings. Fluff the tuna with a fork. Chop anchovy rings with capers very finely. Stir both into the mixture. Finely chop eggs, onions and pickles and mix in. Season to taste with mustard, salt and lemon juice. Quarter and mix in the pearl onions. Sprinkle with parsley and serve.