Myoanatomy of three aberrant kinorhynch species: similar but different?

This is a pre-print of an article published in Organisms Diversity and Evolution. The final authenticated version is available online at: https://link.springer.com/article/10.1007/s00435-021-00519-3 The post-print has open access through the first author's web page https://mariaherranzm.com/publications Open access to read-only published article: https://rdcu.be/ciOg9 (Provided by the Springer Nature SharedIt content-sharing initiative) This project received funding from the European Union’s Horizon 2020 research and innovation programme, under the Marie Sklodowska-Curie grant agreement No 797140 Abstract Aberrant kinorhynchs show several modifications deviating from the typical kinorhynch body plan, including a modified introvert with very elongated and flexible scalids, a weakly developed neck, and a slender trunk with less distinct segmentation. How these aberrant external features are reflected in the inner anatomy and how their aberrant body plan evolved are not understood. Here, we provide a comprehensive and comparative myoanatomical study of three putatively, distantly related worm-like species: Cateria styx, Franciscideres kalenesos and Zelinkaderes yong. Despite the weak external segmentation of the trunk, the studied species show a distinct segmental arrangement of the musculature. However, this arrangement is shifted posteriorly with respect to the external segmentation, because the extremely thin and flexible cuticle is lacking the apodeme-like cuticular thickenings (pachycycli) where the longitudinal muscles usually attach. The muscular arrangement in the three species is overall similar, yet, C. styx shows most resemblance to the allomalorhagid F. kalenesos, whereas the cyclorhagid Z. yong differs in several ways. This suggests a closer relationship of C. styx to Allomalorhagida. Whereas most kinorhynchs prefer muddy sediments, both the allomalorhagid and cyclorhagid worm-like kinorhynchs are mainly found in sandy environments, suggesting that a flexible, slender body evolved at least twice independently as an adaptation to the interstitial environment.Full open access to the Postprint through the author's personal web page mariaherranzm.com Access to full read-only published article: https://rdcu.be/ciOg9 Link to the article: https://link.springer.com/article/10.1007/s00435-021-00519-