Riccardo Levi-Setti, an Italian-born Holocaust survivor who became a pathbreaking physicist at the University of Chicago, uncovering subatomic particles while traveling the world in search of trilobites, ancient arthropods he called “the butterflies of the seas,” died Nov. 8 at a nursing home in Chicago. He was 91.

His son Emile Levi Setti said the precise cause was not immediately known. Raised in an aristocratic Jewish family in Milan, Dr. Levi-Setti was a teenager during World War II, when he hid from the Nazis and their fascist collaborators in a remote farmhouse, a slew of mountain caves and an empty underground fuel container near Genoa.