title: A stem-group cnidarian described from the mid-Cambrian of China and its significance for cnidarian evolution.
abstract: Palaeontological data of extinct groups often sheds light on the evolutionary sequences leading to extant groups, but has failed to resolve the basal metazoan phylogeny including the origin of the Cnidaria. Here we report the occurrence of a stem-group cnidarian, Cambroctoconus orientalis gen. et sp. nov., from the mid-Cambrian of China, which is a colonial organism with calcareous octagonal conical cup-shaped skeletons. It bears cnidarian features including longitudinal septa arranged in octoradial symmetry and colonial occurrence, but lacks a jelly-like mesenchyme. Such morphological characteristics suggest that the colonial occurrence with polyps of octoradial symmetry is the plesiomorphic condition of the Cnidaria and appeared earlier than the jelly-like mesenchyme during the course of evolution.
authors.affiliation: School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea.
authors.forename: Tae-yoon
authors.initials: TY
authors.lastname: Park
authors.forename: Jusun
authors.initials: J
authors.lastname: Woo
authors.forename: Dong-Jin
authors.initials: DJ
authors.lastname: Lee
authors.forename: Dong-Chan
authors.initials: DC
authors.lastname: Lee
authors.forename: Seung-bae
authors.initials: SB
authors.lastname: Lee
authors.forename: Zuozhen
authors.initials: Z
authors.lastname: Han
authors.forename: Sung Kwun
authors.initials: SK
authors.lastname: Chough
authors.forename: Duck K
authors.initials: DK
authors.lastname: Choi
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002681:China; D003063:Cnidaria / Q000033:anatomy & histology / Q000737:chemistry / Q000145:classification* / Q000235:genetics; D005580:Fossils; D010802:Phylogeny