Today, sea creatures known as comb jellies have soft bodies like jellyfish, but their ancestors projected a tougher image: tooling up with hard body parts, probably as protection from predators. In a new analysis of fossils, researchers looked closely at more than three dozen specimens from 520-million-year-old rocks in southern China. Like their modern-day relatives, the ancient creatures had saclike bodies and propelled themselves through the water using eight rows of hairlike structures called cilia. But the ancient species—three that are new to science and three that were previously known but are now being more fully described based on the new analysis—also included eight stiff struts (depicted in white in the artist’s reconstructions above) and eight rigid plates that surrounded a buoyancy-sensing organ called a statolith. (Side views of four of the species are depicted at second from right and in the top row; oblique views of the same creatures are seen at far right and in the bottom row.) It’s not clear what the struts and plates were made of: Although they likely included chitin (the same substance found in the exoskeletons of insects and crustaceans such as shrimp) or a similar material, they could also have included minerals such as carbonates, the researchers report today in Science Advances. Regardless of their composition, the hard parts may have provided both support for soft tissues and protection against predators. And these creatures may have desperately needed protection, the researchers say: They lived in a shallow, subtropical ocean at a time when predators and their prey were locked in an evolutionary arms race. Sadly, the armor didn’t save these ancient comb jellies: They were part of a lineage that apparently died out long ago.