Character_descriptions.docx from The early Cambrian fossil embryo <i>Pseudooides</i> is a direct-developing cnidarian, not an early ecdysozoan
2017-11-28T13:11:28Z (GMT) by
Early Cambrian <i>Pseudooides prima</i> 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 <i>P. prima</i> embryos separates along its mid axis during development, with the transverse furrows between the ‘somites’ unfolding into the polar aperture of the hexa-radial theca of <i>Hexaconularia sichuanensis</i>, conventionally interpreted as a scyphozoan cnidarian; co-occurring post-embryonic remains of ecdysozoans are unrelated. We recognize <i>H. sichuanensis</i> as a junior synonym of <i>P. prima</i> as a consequence of identifying these two-form taxa as distinct developmental stages of the same organism. Direct development in <i>P. prima</i> parallels the co-occuring olivooids <i>Olivooides,</i> and <i>Quadrapyrgites</i> 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 <i>Arthrochites</i> 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 are a vestige of a broader spectrum of body-plan symmetries and developmental modes that was manifest in their early Phanerozoic counterparts.