Developmental biology of the early Cambrian cnidarian Olivooides

Abstract

Fossilized embryos afford direct insight into the pattern of development in extinct organisms, providing unique tests of hypotheses of developmental evolution based in comparative embryology. However, these fossils can only be effective in this role if their embryology and phylogenetic affinities are well constrained. We elucidate and interpret the development of Olivooides from embryonic and adult stages and use these data to discriminate among competing interpretations of their anatomy and affinity. The embryology of Olivooides is principally characterized by the development of an ornamented periderm that initially forms externally and is subsequently formed internally, released at the aperture, facilitating the direct development of the embryo into an adult theca. Internal anatomy is known only from embryonic stages, revealing two internal tissue layers, the innermost of which is developed into three transversally arranged walls that partly divide the lumen into an abapertural region, interpreted as the gut of a polyp, and an adapertural region that includes structures that resemble the peridermal teeth of coronate scyphozoans. The anatomy and pattern of development exhibited by Olivooides appears common to the other known genus of olivooid, Quadrapyrgites, which differs in its tetraradial, as opposed to pentaradial symmetry. We reject previous interpretations of the olivooids as cycloneuralians, principally on the grounds that they lack a through gut and introvert, in embryo and adult. Instead we consider the affinities of the olivooids among medusozoan cnidarians; our phylogenetic analysis supports their classification as totalgroup Coronata, within crown-Scyphozoa. Olivooides and Quadrapyrgites evidence a broader range of life history strategies and bodyplan symmetry than is otherwise commonly represented in extant Scyphozoa specifically, and Cnidaria more generally.Key words: development, embryo, Cnidaria, Scyphozoa, Kuanchuanpu, Cambrian. et al. 2015), the tempo of early animal evolution is astonishing given the scale of innovation achieved (Erwin et al. 2011): the establishment of all phylum-level body plans that are sufficiently distinct that they are effectively defined by the limits of comparative anatomy (Bengtson 1986). Insights into the processes that brought about this remarkable episode in evolutionary history are afforded through comparative embryology of living animals, facilitating inference of the embryology of ancient ancestors and, indeed, into the evolution of development that brought about the origin of animal bodyplans. Inevitably, this approach is confused by the subsequent developmental evolution that serves to conflate homologies and convergences. Hence, the discovery of a fossil record of embryology from early in animal evolutionary history affords a more direct insight into the embryology of ancient ancestors, free from the confounding effects of half a billion years of subsequent evolutionary history. T H O U G H there remains considerable debate over the timing of ori...

A new scyphozoan from the Cambrian Fortunian Stage of South China

“…; Dong et al . ). Accordingly, the preserved parts of Qinscyphus necopinus might also represent periderm.…”

“…Recently, Dong et al . (, ) argued for a coronate scyphozoan affinity for Olivooides . Quadrapyrgites might be the sister group of Olivooides (Steiner et al .…”

“…Review of the lengthy debates on the affinities of these early radial animals is beyond the scope of the present work, as this matter has been addressed in several recent papers (Dong et al . , ; Liu et al . ).…”

“…), Olivooides (Dong et al . , ) and Quadrapyrgites (Liu et al . ) have generally been accepted as coronate scyphozoans, whereas the other hypotheses were rejected.…”

“…), most radial animals are generally accepted as cnidarians (Conway Morris & Chen ; Dong et al . ), whereas Eolympia pediculata is probably a scalidophoran (Liu et al . ).…”