Myoanatomy of three aberrant kinorhynch species: similar but different?

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.

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Data availability

All data analysed during this study is included in the present contribution and its associated files (online resources 1 and 2).

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Acknowledgments

We are grateful to the Bioimaging facility of University of British Columbia, to the Unidade Integrada de Imagens and Laboratorio de Invertebrados from Instituto de Biodiversidade e Sustentabilidade, Federal University of Rio de Janeiro UFRJ (NUPEM/UFRJ—Macaé) for offering laboratory space; and to Center for Marine Studies, Federal University of Paraná (CEM/UFPR) for offering lab space and student support with field collections in Pontal du Sul in 2015 and 2019.

Funding

This project received funding from the European Union’s Horizon 2020 research and innovation programme, under the Marie Sklodowska-Curie grant agreement No 797140 to MH. Sampling in South Korea was funded by the Carlsberg Foundation to MVS (CF17-0054). CLSM facilities were supported by the Villum foundation (Grant # 102544) and the Carlsberg Foundation to KW (CF15-0946). CLSM imaging at the University of British Columbia was funded by the Hakai Institute (Tula foundation) and the National Science and Engineering Research Council of Canada (NSERC 2019–03986) to BSL.

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MH, MVS, KW conceived the study. MH, MVS, KW, TP, and MDD collected specimens from South Korea and Brazil. MH prepared and performed the experiments and imaging at the University of Copenhagen and University of British Columbia. MH prepared all figures and 3D reconstructions. MH, MVS, and KW drafted the manuscript. All authors have proofed and approved the final version of this manuscript.

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Correspondence to Maria Herranz.

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Supplementary Information

Below is the link to the electronic supplementary material.

Supplementary file1 Online resource 1. Movie showing F. kalenesos movement. (MP4 51615 KB)

Supplementary file2 Online resource 2. Movie showing C. styx movement. (MP4 21715 KB)

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Herranz, M., Worsaae, K., Park, T. et al. Myoanatomy of three aberrant kinorhynch species: similar but different?. Zoomorphology (2021). https://doi.org/10.1007/s00435-021-00519-3

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Keywords

  • Mud dragons
  • Segmentation
  • Musculature
  • Meiofauna
  • CLSM
  • F-actin