Is Diurodrilus an annelid?


  • Katrine Worsaae,

    Corresponding author
    1. Marine Biological Laboratory, Section of Aquatic Biology, Department of Biology, University of Copenhagen. Strandpromenaden 5, DK-3000 Helsingør, Denmark
    • Marine Biological Laboratory, Department of Biology, University of Copenhagen, Strandpromenaden 5, DK-3000 Helsingør, Denmark
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    • Katrine Worsaae received her PhD from the University of Copenhagen in 2004. She is now associate research professor at the University of Copenhagen. Her research centers around the morphology and evolution of interstitial and microscopic Annelida—and evolutionary hypotheses such as progenesis. During postdoctoral fellowship at the University of Adelaide, she established a collaboration with Greg Rouse and started a detailed study of Diurodrilus. This cooperative study ultimately led to the award-winning paper published in this issue of the Journal of Morphology.

  • Greg W. Rouse

    1. Scripps Institution of Oceanography. 9500 Gilman Drive, La Jolla, California 92093-0202
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    • Greg Rouse is Professor of Marine Biology and Curator of the Benthic Invertebrate Collection at the Scripps Institution of Oceanography/University of California San Diego. He previously worked at the South Australian Museum/University of Adelaide, University of Sydney and the Smithsonian Institution. Greg has worked extensively on annelid morphology and phylogeny at both broad and fine scales.


Interstitial marine meiofaunal worms of the genus Diurodrilus have always been considered part of Annelida, either as basal or derived, though generally with reference to Dinophilidae. New evidence shows that Diurodrilus has a unique anatomy, and lacks key annelid features, possibly even segmentation. We assessed the systematic position of Diurodrilus among other protostome animals via light microscopy, confocal laser scanning microscopy, and transmission electron microscopy studies of anatomy, focusing on musculature, the nervous system, as well as molecular sequence data. We show that there is little morphological or molecular evidence to support a relationship with Dinophilidae or any other annelids. Diurodrilus has some similarities to Micrognathozoa, though the latter shows complex jaws. On the basis of the configuration of the nervous system and the cuticle we regard Diurodrilus to belong to Spiralia, possibly close to Annelida; however, until further evidence is acquired it should be regarded as incertae sedis in this large animal clade. J. Morphol., 2008. © 2008 Wiley-Liss, Inc.