This undated image provided by the Sars International Center for Marine Molecular Biology, University of Bergen, Norway via the journal Science in December 2013 shows a Mnemiopsis leidyi, a species of comb jelly known as a sea walnut. A new study published online Thursday, December 12, 2013 in the journal Science says comb jellies, a group of gelatinous marine animals, represent the oldest branch of the animal family tree. (Photo by AP Photo/Sars International Center for Marine Molecular Biology, University of Bergen, Norway, Bruno Vellutini)
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