Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom; worm~lab, Institute of Zoology, University of Cologne, Cologne, Germany
Paschalis Natsidis
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom; Department of Biosciences, Durham University, Durham, United Kingdom
Helen E Robertson
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom; Université Côte D'Azur, CNRS, Inserm, iBV, Nice, France
Ferdinand Marlétaz
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
The Arctic University Museum of Norway, UiT – The Arctic University of Norway, Tromsø, Norway
Liam Baudry
Collège Doctoral, Sorbonne Université, Paris, France
Fraser Simpson
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
Eirik Høye
Department of Tumor Biology, Institute for Cancer Research, The Norwegian Radium Hospital, Oslo University Hospital, Oslo, Norway; Institute of Clinical Medicine, Medical Faculty, University of Oslo, Oslo, Norway
Anne C Zakrzewski
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom; Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Berlin, Germany
Paschalia Kapli
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom
Katharina J Hoff
University of Greifswald, Institute for Mathematics and Computer Science, Greifswald, Germany; University of Greifswald, Center for Functional Genomics of Microbes, Greifswald, Germany
Steven Müller
Center for Life’s Origins and Evolution, Department of Genetics, Evolution and Environment, University College London, London, United Kingdom; Royal Brompton Hospital, Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom
The evolutionary origins of Bilateria remain enigmatic. One of the more enduring proposals highlights similarities between a cnidarian-like planula larva and simple acoel-like flatworms. This idea is based in part on the view of the Xenacoelomorpha as an outgroup to all other bilaterians which are themselves designated the Nephrozoa (protostomes and deuterostomes). Genome data can provide important comparative data and help understand the evolution and biology of enigmatic species better. Here, we assemble and analyze the genome of the simple, marine xenacoelomorph Xenoturbella bocki, a key species for our understanding of early bilaterian evolution. Our highly contiguous genome assembly of X. bocki has a size of ~111 Mbp in 18 chromosome-like scaffolds, with repeat content and intron, exon, and intergenic space comparable to other bilaterian invertebrates. We find X. bocki to have a similar number of genes to other bilaterians and to have retained ancestral metazoan synteny. Key bilaterian signaling pathways are also largely complete and most bilaterian miRNAs are present. Overall, we conclude that X. bocki has a complex genome typical of bilaterians, which does not reflect the apparent simplicity of its body plan that has been so important to proposals that the Xenacoelomorpha are the simple sister group of the rest of the Bilateria.
