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Olivooides-like tube aperture in early Cambrian carinachitids (Medusozoa, Cnidaria)

Published online by Cambridge University Press:  29 June 2017

Jian Han
Department of Geology and State Key Laboratory of Continental Dynamics, Northwest University, 229 Taibai Road, Xi’an 710069, P.R. China 〈〉, 〈〉, 〈〉
Guoxiang Li
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China 〈〉
Xing Wang
Department of Geology and State Key Laboratory of Continental Dynamics, Northwest University, 229 Taibai Road, Xi’an 710069, P.R. China 〈〉, 〈〉, 〈〉
Xiaoguang Yang
Department of Geology and State Key Laboratory of Continental Dynamics, Northwest University, 229 Taibai Road, Xi’an 710069, P.R. China 〈〉, 〈〉, 〈〉
Junfeng Guo
School of Earth Science and Land Resources, Key Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, Chang’an University, Xi’an 710054, China 〈〉
Osamu Sasaki
Tohoku University Museum, Tohoku University, 6-3 Aoba, Aramaki, Aoba-ku, Sendai, Japan 〈〉
Tsuyoshi Komiya
Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan 〈〉


The early Cambrian Carinachitidae, a family in the subclass Conulata, are intriguing and important small shelly fossils. Their gently tapering, tube-shaped skeletons consist of convex faces separated from each other by broad, deep corner sulci, and they exhibit triradial, pentaradial, or predominantly tetraradial symmetry. However, the morphology of the aperture and the modes of growth of carinachitid skeletons as well as the anatomy of their soft parts are unknown. Examination of a single new, exceptionally well-preserved specimen of tetramerous Carinachites spinatus Qian, 1977, collected from the lower Cambrian Kuanchuanpu Formation in South China, reveals: (1) that its aperture is connected to a small mass of relic soft tissue and (2) that the apertural end of each of the four faces is developed into a subtriangular lappet or oral lobe that is smoothly folded toward the long axis of the tube, partially closing the tube aperture. Similarities between thorn-like spines on the faces and the oral lobes indicate that the transverse ribs were periodically displaced from the perradial portion of the aperture during formation of new ribs. In addition, the tube walls may have undergone secondary thickening during growth. The growth pattern of the tube and the spatial relationships between the tube aperture and soft parts are analogous to those of co-occurring olivooids. These findings further strengthen the previously proposed hypothesis that coeval carinachitids, olivooids, hexangulaconulariids, and Paleozoic conulariids are closely related taxa within the subphylum Medusozoa. Finally, carinachitids most likely represent an evolutionary intermediate between olivooids and hexangulaconulariids.

Copyright © 2017, The Paleontological Society 

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