This episode page has been compiled from the episode description at the NDR website.
Finchen are to look after Ella's seashell. She has had it for a long time but have been unable to open it, the story says that it contains a treasure. Finchen drops it in a vase filled with water that cause the shell to open up. Muriel, a water nymph appears. She sings a song to Finchen about being underwater and hands Finchen a perl and the disaaper back into the shell.
Ernie has a treasure map of the living room, leading to a spot marked with an X. As Bert watches, he digs up a treasure chest with a letter X inside.