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Worm Palaeo-Evo-Devo-The ontogeny of Ottoia prolifica from the Burgess Shale

Joachim T. Haug and Carolin Haug

Ottoia prolifica Walcott, 1911 is a 500 million years old fossil cycloneuralian worm from the Burgess Shale, Canada, British Columbia. We report newly observed details of the morphology and ontogeny of this species. Previously unknown details could be observed by applying crossedpolarized light. This approach revealed that the tail end is equipped with six hook-shaped spines and that the scalids in the anterior retractable region, the introvert, are arranged in at least 30 radii. Furthermore, an ontogenetic change could be observed: earlier developmental stages have an elongate worm-shaped trunk, while the trunk of adults is pronouncedly bellied. The newly observed details of Ottoia prolifica raise questions about the taxonomic status of other Cambrian cycloneuralians and about existing homology hypotheses for cycloneuralians.