Modern comb jellies are absolutely dazzling with their seemingly unnatural multicolored light shows. But new fossils from China show that ancient relatives of these jellies were beautiful in their own way.

The 520-million-year-old fossils reveal that ancient comb jellies had stunning geometric skeletons that have disappeared over the course of evolution, researchers report in a paper published in the journal Science Advances. These strange skeletons contained eight rigid plates that surrounded the jellies' organs and eight spoke-like structures that radiated outward to surround the soft lobes of their bodies.

The unusual symmetry of these skeletons makes them aesthetically appealing, but it also likely provided mechanical support for the jellies' squishy bodies. It may have aided in defense against predators or other dangers as well, the researchers suggest.

Comb jellies are found in marine environments around the world, but none of the comb jellies known to exist today have a skeleton. In true modern form, they bring us beauty not through amazing architecture but with an incredibly intricate and colorful light display.

All comb jellies feature "combs" of tiny hairlike structures called cilia that wiggle around to propel the jellies through the water. As the cilia move, they refract light in a way that produces these brilliant colors. Up until this study, it was thought that ancient comb jellies had tentacles too, like their jellyfish relatives, but the new fossils provide evidence to the contrary.

Placing comb jellies on the evolutionary family tree has proved to be a challenge, partly because their soft bodies don't fossilize very easily. This discovery of the way ancient comb jellies' bodies were structured is helping scientists settle this part of the tree of life.

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