A new species of a possible thecate scyphozoan Byronia jaegeri sp. nov. is described from the late Katian of Estonia. This new taxon is distinct as it lacks the longitudinal ornamentation present in other Byronia species. Phosphanullus is a phosphatic attachment disk, which has been considered to be a junior synonym of Byronia. We report qualitative energy dispersive analysis and scanning electron microscopy of the composition of B. jaegeri, demonstrating that the tube is organic in composition and has a lamellar microstructure. The compositional differences of Phosphanullus and Byronia do not support their synonymy. It is likely that Phosphanullus belongs to a closely related but distinct phosphatic group of thecate scyphozoans, due to their morphological similarity, but differing composition.
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