The early Cambrian fossil embryo Pseudooides is a direct developing cnidarian, not an early ecdysozoan

Early Cambrian Pseudooides prima has been described from embryonic and post-embryonic stages of development, exhibiting long germ band development. There has been some debate about the pattern of segmentation, but this interpretation, as among the earliest records of ecdysozoans, has been generally accepted. Here we show that the ‘germ band’ of Pseudooides prima embryos separates along its mid axis during development, with the transverse furrows between the ‘somites’ unfolding into the polar aperture of the hexaradial theca of Hexaconularia sichuanensis, conventionally interpreted as a scyphozoan cnidarian; co-occurring post-embryonic remains of ecdysozoans are unrelated. We recognize Hexaconularia sichuanensis as a junior synonym of Pseudooides prima as a consequence of identifying these two form taxa as a distinct developmental stages of the same organism. Direct development in Pseudooides prima parallels the co-occuring olivooids Olivooides and Quadrapyrgites and Bayesian phylogenetic analysis of a novel phenotype dataset indicates that, despite differences in their tetra-, penta- and hexa-radial symmetry, these hexangulaconulariids comprise a clade of scyphozoan medusozoans, with Arthrochites and conulariids, that all exhibit direct-development from embryo to thecate polyp. The affinity of hexangulaconulariids to extant scyphozoan medusozoans indicates that the prevalence of tetraradial symmetry and indirect development is a vestige of a broader spectrum of bodyplan symmetries and developmental modes that was manifest in their early Phanerozoic counterparts.