title: Embryos, polyps and medusae of the Early Cambrian scyphozoan Olivooides.
abstract: The Early Cambrian organism Olivooides is known from both embryonic and post-embryonic stages and, consequently, it has the potential to yield vital insights into developmental evolution at the time that animal body plans were established. However, this potential can only be realized if the phylogenetic relationships of Olivooides can be constrained. The affinities of Olivooides have proved controversial because of the lack of knowledge of the internal anatomy and the limited range of developmental stages known. Here, we describe rare embryonic specimens in which internal anatomical features are preserved. We also present a fuller sequence of fossilized developmental stages of Olivooides, including associated specimens that we interpret as budding ephyrae (juvenile medusae), all of which display a clear pentaradial symmetry. Within the framework of a cnidarian interpretation, the new data serve to pinpoint the phylogenetic position of Olivooides to the scyphozoan stem group. Hypotheses about scalidophoran or echinoderm affinities of Olivooides can be rejected.
authors: School of Earth and Space Science, Peking University, Beijing, People's Republic of China.
authors: Xi-Ping
authors: XP
authors: Dong
authors: John A
authors: JA
authors: Cunningham
authors: Stefan
authors: S
authors: Bengtson
authors: Ceri-Wyn
authors: CW
authors: Thomas
authors: Jianbo
authors: J
authors: Liu
authors: Marco
authors: M
authors: Stampanoni
authors: Philip C J
authors: PC
authors: Donoghue
mesh_terms: D000818:Animals; D003063:Cnidaria / Q000145:classification; D004447:Echinodermata / Q000145:classification; D005580:Fossils; D010802:Phylogeny; D012098:Reproduction; D037401:Scyphozoa / Q000033:anatomy & histology / Q000145:classification* / Q000196:embryology