The Early Phylogeny of Chordates and Echinoderms and the Origin of Chordate Left–Right Asymmetry and Bilateral Symmetry

@article{Jefferies1996TheEP,
  title={The Early Phylogeny of Chordates and Echinoderms and the Origin of Chordate Left–Right Asymmetry and Bilateral Symmetry},
  author={Richard P.S. Jefferies and Nigel Brown and Paul E. J. Daley},
  journal={Acta Zoologica},
  year={1996},
  volume={77},
  pages={101-122}
}
Left–right asymmetry in Dexiothetica (= echinoderms + chordates) results mainly from dexiothetism—an episode in their ancestry when an animal resembling the Recent pterobranch Cephalodiscus lay right-side-downwards on the sea floor. Castericystis sprinklei belongs to the dexiothete stem group. The history of the echinoderm stem group is reconstructed. Chordate bilateral symmetry evolved by six successive steps. Tail–head overlap occurred independently in craniates and acraniates. The neural… 

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