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Journal of Paleontology 91(5):871–882
solenial pore system suggest that Cambroctonconus was a basal member of the octocoral clade, and thus represented an early calcification event in the phylogenetic history of Octocorallia. In traditional morphological and rRNA genomic classifi-
cation (Collins, 2002, 2009), Hexacorallia and Octocorallia are sister groups within Anthozoa, which itself is a sister group of Medusozoa. Kayal et al. (2013) rejected the monophyly of Anthozoa following phylogenetic analysis based on mitochon- drial genomics, and placed Octocorallia closer to Medusozoa. They suggested that Medusozoa (Scyphozoa+ Hydrozoa) formed a sister group to Octocorallia, and that these together were a sister group to Hexacorallia (Kayal et al., 2013). The phylogeny was cited as potentially supporting the ‘polyp before medusa’ hypothesis of cnidarian evolution (Ax, 2012), a theme taken up by Dzik et al. (2017) in the context of the fossil record of the tubular cnidarian Sphenothallus Hall, 1847 and related Lower Paleozoic taxa (Tynan, 1983; Van Iten et al., 2014). Zapata et al. (2015) restated the monophyly of Anthozoa,
Octocorallia, and Hexacorallia. They admitted, however, that the combination of the deep history of some crown groups and extensive record of fossil extinction events provides a substantial hinder to the reconstruction of cnidarian phylogeny. It is an obstacle that Cambrian fossil cnidarians, including Cambroctoconus, can help to overcome.
Figure 5. Schematic cross-section of Cambroctoconus koori n. sp. showing development of the porous calcareous skeleton within the mesogleal layer of the coenenchyme.
Cothonion by Jell and Jell (1976). This observation is consistent with the present interpretation of the corallum wall as formed around the gastrodermal solenia within the mesoglea (Fig. 5), as in the octocoral Epiphaxum. It is supported by the occurrence of secondary calices branching from the primary calice in Epiphaxum, which arise from the mesoglea filling the channels on the outside of the calcified polyp wall (Bayer, 1992). However, Park et al. (2011) compared the skeletal walls of Cambroctoconus with cnidarians in which the outer corallum wall is a true epitheca deposited from the epidermis and not closely integrated with the mesogleal polyp tissues from which new individuals arose. This comparison was cited as evidence that mesoglea (jelly-like mesenchyme of Park et al., 2011) was absent in Cambroctoconus, which was considered, therefore, to represent a stage in cnidarian evolution earlier than the acqui- sition of the mesoglea that is characteristic of crown group cnidarians (Park et al., 2011, fig. 4). Thus, Cambroctoconus was interpreted by Park et al. (2011) as a stem-group cnidarian. However, the present interpretation that the outer wall in Cambroctoconus formed within the mesoglea (Fig. 5), as is the case with the calcified calice walls in the octocorals Epiphaxum and Nanipora, demonstrates that a mesogleal layer was present in Cambroctoconus, refuting the argumentation proposed by Park et al. (2011). Description of gastrodermal solenia in Cambroctoconus
promotes recognition of the three-layer coenenchyme that is diagnostic of cnidarians (endoderm + mesoglea + ectoderm; Fig. 5). In this feature,Cambroctoconus is typically cnidarian and not a pre-mesogleal stem-group representative. When considered together, the octagonal form, eight-fold septal symmetry, and
Acknowledgments
H. Agic and A. Kouchinsky made some of the SEM images. J. Botting, A.B. Smith, and
A.Yu. Zhuravlev gave valuable sug- gestions and pointers to literature sources. T.-Y. Park provided illustrations of Cambroctoconus orientalis, information concern- ing the relocation of museum specimens, and reviewed the sub- mittedmanuscript. R. Elias is thanked for information concerning calostyline corals and for reviewing the submitted manuscript.
References
Ausich, W.I., and Babcock, L.E., 1998, The phylogenetic position of Echmatocrinus brachiatus, a probable octocoral from the Burgess Shale: Palaeontology, v. 41, p. 193–202.
Ausich, W.I., and Babcock, L.E., 2000, Echmatocrinus, a Burgess Shale animal reconsidered: Lethaia, v. 33, p. 92–94.
Ax, P., 2012, Multicellular Animals: a new approach to the phylogenetic order in nature, volume 1: Berlin, Springer Science and Business Media, 225 p.
Babcock, L.E., 1994, Systematics and phylogenetics of polymeroid trilobites from the Henson Gletscher and Kap Stanton formations (Middle Cambrian), North Greenland: Grønlands Geologiske Undersøgelse Bulletin, v. 169, p. 79–127.
Bayer, F.M., 1956, Octocorallia, in Moore, R.C., ed., Treatise on Invertebrate Paleontology, Part F, Coelenterata: Boulder, Colorado and Lawrence, Kansas, Geological Society of America and University of Kansas Press, p. F166–F231.
Bayer, F.M., 1973, Colonial organization in octocorals, in Boardman, R.S., Cheetham, A.H., and Oliver, W.A., Jr., eds., Animal Colonies: Stroudsburg, Pennsylvania, Dowden, Hutchinson and Ross, Inc., p. 69–93.
Bayer, F.M., 1992, The helioporacean octocoral Epiphaxum, recent and fossil: a monographic iconography: Studies in Tropical Oceanography, Miami, v. 15, p. 1–76.
Bayer, F.M., and Muzik, K.M., 1976, A new solitary octocoral, Taiaroa tauhou gen. et sp. nov. (Coelenterata: Protoalcyonaria) from New Zealand: Journal of the Royal Society of New Zealand, v. 6, p. 499–515.
Bengtson, S., 1981, Atractosella, a Silurian alcyonacean octocoral: Journal of Paleontology, v. 55, p. 281–294.
Bengtson, S., Conway Morris, S., Cooper, B.J., Jell, P.A., and Runnegar, B.N., 1990, Early Cambrian fossils from Australia: Memoir of the Australasian Association of Palaeontologists, v. 9, p. 1–364.
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