1) Peel the oranges leaving just 2 segments for garnish. Peel the grapefruit. Chop both the fruits.
2) In a bowl, mix the fruits with cheese and cucumber.
3) In a different bowl, mix the crab meat with mayonnaise.
4) Keep the crab meat mixture on one half of each of 4 scallop shells. Keep the fruit mixture on other half.
5) Decorate with orange and parsley. Serve chilled.