What surname is shared by the acting brother and sister whose real first names are Jacob and Margalit?

Margalit Ruth "Maggie" Gyllenhaal (born November 16, 1977 in New York City) is an American actress. The first name on Maggie's birth certificate is "Margalit", which she did not discover until 2013, when adopting her husband's surname. Margalit is a Hebrew word meaning "pearl"; some news stories have spelled it "Margolit". Part of the Gyllenhaal family, she is the daughter of filmmakers Stephen Gyllenhaal and Naomi Achs, and the older sister of actor Jake Gyllenhaal.

Jacob Benjamin Gyllenhaal was born in Los Angeles, California, to producer/screenwriter Naomi Foner (née Achs) and director Stephen Gyllenhaal. He is the brother of actress Maggie Gyllenhaal, who played his sister in Donnie Darko (2001). His godmother is actress Jamie Lee Curtis. His mother is from a Jewish family, and his father's ancestry includes Swedish, English and Swiss-German.