Cassiosomes Viewed under a Microscope (IMAGE) Smithsonian Caption The oval structures along the protruding edges are stinging capsules known as nematocysts, and the brown cells in the interior are symbiotic algae that live within the tissues of Cassiopea, or upside-down jellyfish. A team led by scientists at the Smithsonian's National Museum of Natural History, the University of Kansas and the U.S. Naval Research Laboratory report in the Feb. 13, 2020 issue of the journal <em>Nature Communications Biology</em> that they have discovered microscopic stinging structures inside the mucus secreted by upside-down jellyfish--gyrating balls of stinging cells that they call cassiosomes. These cassiosomes can sting swimmers and prey without coming into contact with the jellyfish themselves. Credit Cheryl Ames and Anna Klompen Usage Restrictions News-media use of these photos in relation to this study is permitted with attribution. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.