Intraspecific variation of radial symmetry number of a 535 million-year-old jellyfish

•First report of intraspecific variation of radial symmetry number in early cnidarians. Although modern jellyfishes are stably tetramerous, intraspecific variation of radial symmetry number is not uncommon and spans from unimery to octamery. However, intraspecific variation of radial symmetry number among fossil cnidarians is rarely reported. We report a single new specimen of Quadrapyrgites quadratacris from the Cambrian Fortunian Kuanchuanpu Formation at the Zhangjiagou Lagerstätte in southern Shaanxi Province, South China. Quadrapyrgites quadratacris has previously been interpreted to be a coronate scyphozoan with stable tetramery. The new specimen has morphology well comparable with the previously reported specimens of Q. quadratacris, with the exception that it is pentamerous. This is the first report of intraspecific variation of radial symmetry number among the Fortunian cnidarians. It demonstrates that tetramery is stable for Quadrapyrgites, with pentamery as less common intraspecific variation, and that the Fortunian scyphozoans have acquired the ability of regulating and changing their radial symmetry number during their alternation of generations.